In what ways is the word “work” as used in eveaby6 sanbe8;py)vs 5s4cj 4d3ryday language the same as that defined in physics? In wsbpna 54e; 4)d3bsa8csyyvj6 hat ways is it different? Give examples of both.

Can a centripetal force ever do work on an object? Expe.8o uoi3 1kxllain.

Can the normal force : w5e,d -ms *.:ma vy6rn5 uqoz.mzmfoon an object ever do work? Explain.

A woman swimming upstream is not moving with(zui4oz+g4tt/ ,t q2s 48hj)fseex jb respect to the shore. Is she doing any 4s)jqt/(2 u+gjo b 44zeez,fxtis8thwork? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Cme y88. *o hcfbu.pcv5onsider what happens to the dishes when you pull a tablecloth out frfv yom.cc*u5h ep.b8 8om under them.]

Why is it tiring to push hard against a solid wall even though o2lue9d3 ty4v75w o5xrar2gd you are doing no woag24vdly75u3 r or2xo5tw9 edrk?

You have two springs that are identical except that spring .noz89 8qatjp l is stiffer than springon89.tq8 azpj 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is fred4xapg h r(8(q(mqa 4te to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has tra p(d(ahgq4xrqm4t8( aveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitationa (ghrdl twt+; f3)gx/al potential energy change when you jumpw 3tg at/hl g;(df)x+r as high as you can?

In Fig. 6–31, water balloons are toszrh28x5m6 . ks3hw kjssed from the roof of a building, all with th h5kz wjhmsrk6.82 3xse same speed but with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest poix6g.db ke)( n:gbbw1gnt in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilkn(6)gw:.g bbg d 1exbibrium position? Explain.

A coil spring of mass m rests upright on a table. Im95 mo0u 56sw9q.yth miis 0iif you compress the spring by pressing down with your6y59i0i5 shqwmm iu0mt i9os. hand and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The instru 0qfiylg jr dsy7 0q rb4fn1q889:yh9bctor pull8 q:9byjs0bqif80drfhg 9y 4qr1ln7ys the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potentiad.y+y.ppdl p; 8xw*zhr, ytb .l energy when water at the top of a waterfall fayt pl.,bh*+rpz. .; dwd8pyyx lls to the pool below?

Describe the energy transformations when a child hops around on a pogo stick ,3ylehi)ks, a.

Describe the energy transformations that ta*sulh6 gdq.r9f.w0; c s5p .kfmzmfs(z1v (wc ke place when a skier starts skiing down a hill, but after a time is brought to rest by stzvsf z(wcf s gm q;.rdf.0( kh9c5m.uwl6*1 psriking a snowdrift.

A child on a sled (total muyyy(z et 0f.;ass m) starts from rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and ther.0yt; u eyyf(ze is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rather hqyx im8c/ a+zr7h4f6 than stepping o ac4 hh6xmqz7y+8r f/in top and jumping down on the other side. Explain.

Two identical arrows, one with twice the speed r m*litmc.v0p: m/f1 zof the other, are fired into a bale of hay. Assuming therml0:c*z.1m tv i fpm/ hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of ene6pf 4(l-d7ss pjhol 5 jtal xa3x6/+xurgy, (a) ignoring friction 6lx3pfsxusa/(p jh +7xa -d4l 5lt6jo, and (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is droppyond1 ug1 /pa7ed, can it rebound to a height greater than its original heanou17dy1p g /ight? Explain.

Suppose you lift a suitcase from the floor to a table. The word;5z jmfa7x9 v+ npp/r)u ,wwuk you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, andp ,5pd 7x+a funwj)uvw9r;mz/ (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than t:r4m-elyev117t y b xkhe work.

Why is it easier to cli+hj5nx/6 qcrgo 7/tb hmb a mountain via a zigzag trail than to climb straight up? tqxgcn+j/o5/rh7h 6b

Recall from Chapter 4, Example 4–14, that you can use a pulley ank *;16lks+ruh :fs9swbv bd7g d ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much ropeuvs dk1s9 +*;g kf:wsbrlb7 6h must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitlciy+: fg 06dtational force when a 265-kg pile driver falls 2.8+ c6y: g0diftl0 m?    J

  A 65.0-kg firefighter climbs a f 0(pk :k+n+g1o:-ht)w 8 puifbe6ojcgfud7b ylight of stairs 20.0 m high. How much work is requwo:y):8ugj fdke-p + ogbchu0pk7t1b(ni+ 6f ired?    J

  A 1300-N crate rests on the floor. H)u okn;z);wwtbpvh u-x4+b*b*xf ob+ow much work is required to move it at constant speed (a) 4.0 m along the floor against a friction forczkv+)hu-bt)x u*w +p;bwx 4o o*b;fbn e of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the move*a9:oare(m v/e1zai d3)mzwu sy t9,c rs do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without 3*:s9 z,e1ar (a/)ym aw evmcodiz9ut acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force ac(g9q v ax9u 7zlko(d0kgv4.d sross a floor at a rate of for 7.0 s. Find the na0g9ogl( v sx4.dkd 7zkvu9q (et work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on juqop 0u:u/ -e+cw0 6;liejjt a table. How much work is required to stack them one on tp /j t0oi-uwj 0uj:; ele6c+quop of another?    J

A lever such as that shown in Fig. 6-35 can nn)o, uac3m+ z,2puoj be used to liff objects we might not otherwise be able to lij3 2pu nz,a uc)+,moonff. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 mg z9v,h* /voxld6 cih0 down a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calcula0cd* h/hlv o9gi v6,zxte:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter of mass M an acceleration ofpsrw8 o*p,rns e*to5:g*k9 po 0.10re s*o*w5rptn :o skop9g8*, p g upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

  $\text{What is the minimum work needed to push a 950-kg car 810 m up along a 9.0$^{\circ} $ incline? }$$(a)\text{ Ignore friction. }$    J
$(b)\\\text{Assume the effective coefficient of friction retarding the car is }0.25.$    J

  In Fig. 6-6a, assume thetp-ypc:uk 3e l 2h7.zary,e /v distance axis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as ,cln u/r/4lv9i*c1d s don4gx shown in Fig. 6–37. Determcol4 /9dxul,* rg4ids1cnv / nine the work done by this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

  A spring has $k=88$ N/m. Use a graph to determine the work needed to stretch it from $x=3.8$ cm to
$x=5.8$cm, where $x$ is the displacement from its unstretched length    J

  The net force exerted o qvo1jg sar:5 a4n,j,qn a particle acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule,) s5lgx:w 4ase4+bddp with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is (c)fa h)*yr/2 hw tifmdoubled, by what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an ele.2cos tb2e gga2 e5l)nctron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar tgx8+ r7p.ky mphw 26fstp-/fzraveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose s5k)t7 ltu2ztl w a/*wktring exerts an average force of 110 N on the arrow over a distance of 78 /ktl7wt2ak) u *lt z5wcm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backwx.y v j/nen ktrr2ce19 m-px783gv(tu ard 25 cm when the bxje vtc 7 1np u(-k8xgv2/trrnm9 y3e.all is caught. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor wi 6z t2,o e exf ovg;ys+sr51x(+vym1vpll its minimum braking distance be increased, assuming all elsv esyxoeg1r52t+6o,xz y 1;v+ms(p vfe is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road,ksr.wzczp b jg5 u7 br/c..27d investigators measure a car’s skid mark to be 88 m long. Therg7dz5c7b .k .u2j.rw/zpscb accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitchtk,/6tx c , u2fhra a0les4w(9dtnu x-ed at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is abo(t sx rf0d 2tc,x49ht/u - 6,aulwkenaut 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who dozkrp/f0g 4u cc/u o)f3 mgo*o6es 80.0 J of work on it? Negloo0g)rc up/ 3*/m46fogufzkc ect air resistance.    m

  A 285-kg load is lifted 2(zb05 ebbg *+z 4ehhxi2.0 m vertically with an acceleration by a single cable. Determine5ezh bxg0eh*4b(+zi b
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m Hjv.cwd4-7 dc uow much must this spring be stretched to storvdjd-u. 7cc 4we 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to6zh4aqfj / l2svx+/ht another 1.2 m higher. What is the change in potjf+v 42lq/st/xhah6zential energy?    J

  By how much does the gravitational potential l 7ras4uvnti,k4jfpo 2 *:)mb energy of a 64-kg pole vaulter change if his center of mass rises ab a)os:,rj4flpmu n bv*k427tiout 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speev5ibbw3k7ta4tf a3: q d v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance o7av5 3:4btfi t3aqb wkf 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person liftyx3c rwbwu0b20sq*s ko zw;,(s a 2.10-kg book from the ground so it is 2.20 m above the ground. What is the potential energy of the book relati2r qcy,ws* 3okb uz0 ;bws0wx(ve to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and cli)urot cqu- 5j 5+sb(ccztw05y mbs to the top of a 3300-m peak5(0y)5jrc octq zt wsuub+5- c.
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically next to a ruler. The end of the sprin 3.uv3revnn n um.l:wqm861rag is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now atta8:a mvuln61rne.33rwv.q m un ched to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grab -66vv;hxtt ,hruznv : )7j b7dxms3nrs a vine hanging vertically from a tall tree in the jungle. Ho vx6rvhx-udr vn msz;,b 7n6t7j):3htw high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, startin4k9q /*qg7a afik1 lkjg from rest, slides down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a fricti(i5mkk4q n9wk onless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed i 8y3cid+7 lezsq9; dhxnto gravitational potent9 cdde+yiqlz3xh7;s8 ial energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertica *fuize.n b*y/ g7 ;-tfkffsm0lly upward from the top of a platform with a speed ;m/ f -.ftibyu7e f* *s0kngfzof 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

  $\text{A projectile is fired at an upward angle of 45.0o from the top of a 265-m cliff with a speed of 185m/s. What will}\\\text{be its speed when it strikes the ground below?(Use conservation of energy.)}$    m/s

  A vertical spring (ignore its mass), whose spring stiffness constant x( 3/n(ehzeysq)+ td fis 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it g+ny(3/s d)h exqtfez (ive to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction woow dk; -3)yyz;pd m0od/vx2hkl6 v4along the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radiu0dly;4xz3d vo- )wk;ohd 6p y wo/2kvms is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffness /ks8ea*1. fut0 t7hxzx4xoz k constant k), Fig. 6–40. The block is given an initt/u84*sxzkka . 71xxzo0ef t hial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. Sftrxt*r (k3rov +sj 0m;+how -he is tied to a bungee cord whose unstretched lengr *orr3- 0x;sw h(o tj+ftmkv+th is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car sxup78d0 g. 8 5tonzxydhown in Fig. 6–41 is dragged up to point 1 where it is released from rest. Assuming nd78ox xyndp0tug5.z8o friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed o8+qkk7dha - -nwxvcxsg q-x0(f 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the botju )9i9s, z:jh:pwr(7zem u fitom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k shoul j) pi :sfu99 wuirmz:(je,z7hd have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up a 7 p3v0y62ii urkc5t99g4w hxjf.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 954 9 s0gx8i +b 2j7tf gajh,w1u0ovdauwkm/h in opposite directionsufhw+1as07xg ,jt8 biwd4v ag oj0u29, collide head-on and come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and axz;j /oi3ns 4reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generated in this proceso; j i3xnza4/ss?    J

  A ski starts from rest and slidq z)1mlnagt/le-zzt+ ln8j9 *es down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a lc1cep;mpw -z44l oe p6xs-2ztree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, andp0sj7knx)3 w.2l te2l,sw abm it bounces back to a height of 1.5 m.2)els72w3m tp s, kxbalj nw.0
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is+.bfrb3 0x(5lacu,cftiw o 10qhoqq, pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the,5b3c,txi f aof0q q (1wb0+co.ql urh coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed bc4s(5s05 + ,j2lxcu12cizwj xjxiub of If the average force of friction is equal to one-fifth of its weight, with whaw5 l0j4x 1 jc2ic(ij5 ubcz2,sb+ uxxst speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a s rnt i4bb q4:t.6dvh8lteady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attachtdfa3 n,iud: 1ed to a very light horizontal spring (k=180N/1if3,nt aud d:m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal iqqum.sid0 )me83ep9* 8tw dy 4 tgkx0spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A qkut0 4 y.xm d38ies wte0p9mdqi*g)8force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle us:*h ou 8g mz9ahy7vo9ped a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of o ua 99v7opmy8:hzhg *3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a sixth-story winm*t me)9tuui y3(6duzdow tzuuemmu) (3td6 9 i*y16.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h wh)t vybevfa sk05 5;u,gat must be the average force exerted on the car due to friction and air vy;e,b5f)k guv0as 5tresistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. Whatwk +i1 u.vw/zs is the average p+vwsw1 /ki. zuower delivered by the engine?$\approx$    hp

  (a) Show that one Bry g,b,+re5)4o3hzjbwc b /bxnitish horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are oft.-cw hsp +o kmmgz:+.pen expressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 65km/h in about 6.0p2 -yr/ 4vsuja s on the level when it is in neutral. Approximately what power (w2 u/arj4pyv s-atts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor x6p w(y7vo;zli3g0s q do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14 y4wno k b7ph8e.i-+ +ey;ccgtm/s If this motion takes 1.beige cy+ ;y4-.7p +8tokcwnh5 s, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.6ep/m3 i)wryq8n rw8b1 0 m. What output rating (watts) should the pu3r/)81ym w pebqn rwi8mp motor have?    W

  During a workout, thevgvq* u m2j5rz3pw-u0 football players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined at an angle ofq*jwg z35v purmuv02- 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist clim.,/zyso mqk4(9;r*yqfc8vvfv uy ,gsb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output 9mn * g+f87r(ov9vdv hluz,ayof 120 hp. How steep a hill can it climb at a constant speed of 75km/h if7v d n8lu(fhyr9ao ,m*g+9vvz the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a a da mc)zh p911( kpzqkv78ug5310-kg box along a level floor at a speed of 1a1kvpq ( 87hk zd5)czgupm9a1 .2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.: 3 uw1zvqza84lte0h- swpu. fwd7qj/0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars hav5 m(5zv.)ehn vxfu. a+a0hipa y ce+0ee built “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, asahpv +.fv(mee0 +5x5ia hcz0 y)aen.usuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library tg2hayzp70t(jc3 l/pu-n) pzohe first shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all p0plu-nch zta) /32 j yozg(p7laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’ ; q;umrppep(b4 .6 gp/.12jsu(n jlav-aavbys famous long jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he u jeb g(q2.vp. raab4 j1s6pan(/mpvup -yl;;need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without frictionjcy,j uy)1tx e s5f5 p0+gtd;r along the looped track shown in Fig. 6–39 is to remain on the track at alsy ,)+5cjjgu5xd p1e t fr0ty;l times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft without q3 hyma 6y. : 9a*iihv:pmc2nchis parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries.imqaimc. *hcn2v9a6 yyp:h3: Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose other end is a*tl g+ ddf;o,fixed (Fig. 6–4a;gto, ld+d* f3).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountain. The climb is mavegz5c; z .8hxy;9xb mde in 5.0 h starting at an elevation of 2300 m. C;.g 5 ;xzvhybxc e9zm8alculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m above /gqa tk)8ls64 1xt+aqllj 9svl*cez(a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims thatszos zllk 16oip 0xlo86zo +*6 its lifts can move 47,000 people 61zo ooo0 l6k6s sxpil+*8z lzper hour. If the average lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls ve1 mac*,ba b1/.ho.b fgvz4u lndj9cv0rtically 81 m before striki m0fdba9, o./hjb4 uv*bv1.a1 cgc zlnng the turbine blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (Fig. 6–44), the di. g4s.:-p9 wrqcwkkgybxm6+bfference in your apparent weight at the top of the circular loop and the bottom of the circular loop is +b. smc ggbr4yw9:-kwp.k6xq6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly into work, how hh:/ jfnwto bu, -zt:ygasvg, -r* p2(high could an 82-kg ma: vtf-tzbgy jwaoh-:2n *p/s(,,uhrgn climb a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward awq+iq+t9 :nd l. /jkcungle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the scak mnu6)w )tkg*m 7e0chle compresses 0.60 mm, and it tells you your weight )m*7 mn0c)tkue k ghw6is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabeyz1 ivb*d8 p5s a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his velocity is85ei b1zpdv y* zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg.a 1i)am ju 5mr)y,3hh0a 4n,nqsizc y athlete climbs a vertical distance of 5.0 m in 9.0 s. What min n4a)hrihnymz3c 1 us iaa.y0,),jm q5imum power output was used to accomplish this feat?    W

  Some electric-power gqtamsp;zyer 07( z x+m70un,companies use water to store energy. Water is pumped by reversible turbine pumps from a lowq+etmpx0n7 a (,rygm70s z u;z to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constangpy:qjylj) 7-2sadh: t k is cut in half. What is the spring stif gljjy-s 72:p:yqdh a)fness constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rougokzd g.7y)l .k,xh cb7pz8) fgh 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 s, how long will b-c4 2o 1llkv5o6zmo vn, kl5wit take to accelerate from 55km/h to 75km/h Assume the power stays the same, and nez55 coo1 owbl2 n,k4lmv-k v6lglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient waljtfw t +h2z -lb,a7-jmks on an inclined treadmill (Fig. 6–46). Estimate the power require+-a-jjtt fhwl27 mzb, d from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews r j:h5j3(7 a p6r ab)zhnmap/pa 500-kg rock vertically upward a distance of 500 m, what was its velocity when it left the volcano?pjpz:)5aj( aphr 3/n 76mhrba $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a rate 0m(f+g.arg0)n;onnbjc v j70 rgr6m jof 95kg/s (a) If this water wheel is set up to provide electricitrac)7mog+nm 6n 0j0(nr. rbgvj j;0 fgy output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s