In what ways is the word “work” as used in ev/svup 0wp 35lkeryday language the same as that defined in physics? In what ways is it different? Give examples of5vsw/pu0p3 kl both.

Can a centripetal force ever do work on ayl8t.cp+ wvs9 s3fe zb/ob.z1n object? Explain.

Can the normal force on an object ever d-vt4o2r wds k9o work? Explain.

A woman swimming upstream is not moving with respect to the shore. Is she doi tkc piu+u r q9d5; jc8l3-lvw1u)6gjlng any work? If she stops swimming an;u - cc 5gvtjq6)dl9u31purjll8 wki+d merely floats, is work done on her?

Is the work done by kinetic friction fo+hya bcy-x7f 7rces always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out from under them.]b+7ac7 yhx yf-

Why is it tiring to push hard against a solid wall even th6.g7 vzo/bx irough you are doing no woriz.gxr7ob6/ v k?

You have two springs that are identical exc y9-xpzl).ab)5tqtts ept that spring l is stiffer than spring 2)-q.tsbp)zy5att x9 l $(k_1>k_2).$ 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 free to st : /qt3m w0*s(fwdieflide on a frictionless surface (Fig.6-30). The blodt f tw(3 0msfwie/*:qck starts from rest at þoint A, and by the time it has traveled 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 gravitational pote 26yjeugk;dc, ntial energy change when you jump as high as yo6;gj2de,c k yuu can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all fp1aw( jon) 6bwith the same speed but with different launch angles. Which one has the highest sp)1awfpnj( b6o eed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lcj18ct0 )dwin; id4al owest point 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 caus4l;a cd8cd in)jwt01i e it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a tablwo7:p5 ee 7uroe. If you compress the spring by pres7:wpu5 o roee7sing down with your 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 v;:-glnt9lj o wire (Fig. 6–33). The instructor pulls jg t-ll: v9;nothe 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 p :d83 +qmmpb-qt5jh uo7 set;zotential energy when water at the top of a waterfa3tsjq87 e5 :m;+bm p- qouzhdtll falls to the pool below?

Describe the energy transformations when a child hops around on a pogo s;;ihm, kfm0mpii ) m;htick.

Describe the energy trasmtm)v6mbt5b,) y5k ) u/cxdtnsformations that take place when a skier starts skiing down a hill, but after a time is brought to rest bys)u6 vyb)tb5mdtmc)xm,/ k5t striking a snowdrift.

A child on a sled (total mzdh .ihg(ni,+ass m) starts from rest at the top of a hill of height h and slidi.ghn d hzi,(+es down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a falle0x3lr vwmu+uen 3u t4(n log in their path rather than stepping on top and jumping down on the other side.v+ w ut0(3 3xnm4reulu Explain.

Two identical arrows, one with twice the speed of the other, are fptv g0scrhmk (4,(8l xired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the spv r (gk 0t(xclh,sm48lower arrow? Explain.

Analyze the motion ofqj: ,)+zcc nau a simple swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction uc+j )nzqc:a,into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height gr,(w6 9s3r mmhkwqcr;ueater than its original height? E(3r wr;m qk ,9swuc6mhxplain.

Suppose you lift a suitcase from the floor ton59py*k 4 tysk2ae 5tk a table. The work you do on the suitcase depends on which of ttkt *9ekya2py 55 n4kshe 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, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed r. 8 s/5pbbynmfather than the work.

Why is it easier to climb a mountain via a zigzag trai (8vvm.v /ohbs2h v-fwl than to climb straight up mv2 (-s/vh.vof8bvhw?

Recall from Chapter 4, Exampl)w.ioo4 n.nl ke 4–14, that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for evo.n wnko).l4i ery meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pi6 rh3ycee .v yo8z9hs(le driver falls (ey3o ey .hsz6hr89cv 2.80 m?    J

  A 65.0-kg firefighter climbs i)m x.*vuj/l -a vn91bgt;p tva flight of stairs 20.0 m high. How much work is required?anm/gi1v.vp*;vj- lx t) b 9tu    J

  A 1300-N crate rests on the fo1 m db7xckaa:kh )9oo6b1d w8loor. How much work is required to move it at constant1h axb9b7c8 a1:dk)ookodm6 w speed (a) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did thep + k9o8ojjsr: movers do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acces 9k8rj+jpo o:leration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg i )8tyl;r eh frzj3zr7d ,9cc:us accelerated by a force across a floor at a rate of for 7.0 s. Find r9rr);ycc8 l,jtd z:7hfe zu3the net work done on the box.   J

  Eight books, each 4.3 cm thick with rjyj5n,+mkt9 g23o.+zc zx0xi pg)zy mass 1.7 kg, lie flat on a table. How much work is required to stack them one zjtzjpz )2 5 giy+x3o c90kymn,rg+x .on top of another?    J

A lever such as that shown in Fig. 6-35 can be used tospocsy 6 a0 xzdg)ai:go6 ; i;-m,e.oi liff objects we might not otherwise be able to liff. Show that the ada60ig: ;z gy,osm ei)ci.6 o-p;soxratio 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 m dosn3f f+j-l* hzwn a 28° incline and is kept from accelerating by a man who is pushing back on it parallel -lzh nfsf*+j3to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(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 du3fk9r9b ug-acceleration of 0.10 g k f dbru39u-9gupward.    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 the distance axis is lineae+73n nxy*v,bdl-vthq.j )gc : 3gv uqr 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 shown in Fig. 403dm0 8*fcb eyobye,j lq+id6–37. Determine the work done by this force to move the j *0qc4l d3i bfyb,e+80y doemobject (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 on a particle acts in 9gp-s77 qxps*xkq x k5the $+x$ 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 ox +l5fxvfsi k7-f6i:qrygen molecule, 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 doubled, by what factorn+8bribr 837/w dqlrw 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 elez fb (-n9qyvtbcb4f h7a rl72,ctron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 travezmy-- r yhyp,q: -eb+w3 fvit hr7u56zling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose str0h3 )vgu8rsk ging exerts an average force of 110 N kh 08rsu3gvg) on the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 3s8x 9uq/vh kap vx+b,d33nim32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the 8phmxvb 3qx 3/,+iv 93usda knaverage force exerted by the ball on the glove?    N

If the speed of a car is incraao(5y-o h;ms b1 pv.xeased by 50%, by what factor will its minimum braking distance be increased, assuming all else is th-(mx;shpvo y b 1a5.oae same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investiga3x /v/zfhi ncguub9 9: ,hmkr)tors measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic frictih9/:f)iv, /ugkbcm3u9h nxz ron 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 0.2xg rznpa:kzk0 jvy0b28:y)n1b 5 ga(h5 kg is pitched 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, n0r1vh z8x2) ypkg:bj(aa:gk50 ynzb if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thro5jjdovq j:3d3 wn straight up by someone who does 80.0 J of work on it? Negjd5 jodq jv:33lect air resistance.    m

  A 285-kg load is lifted rlc8w/5 b*xgw 22.0 m vertically with an acceleration by a single cable. Determ bg85wlr*wc /xine
(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 qnblb2k cse24 d4nlx 40eh3a6 How much must this spring be es6hc2nekq0 d 4a34l nxb24l bstretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to abp xyb+u b6ao 71zc/oy)a rs0-nother 1.2 m higher. What is the change in 1yrx+a0p/b6 a-uo cys)7b zbo potential energy?    J

  By how much does the gravitational potential energy of a 64-kg pole vaulter c4gc;lm2oik ) r0ow5,8w (nq natzy* ephange if his center of;o)z5lm2nwa, 0qkywrn(8 g *oe4pci t mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horit8daet 3 n/7e+q6cpcq zontal surface has speed v = 65 km/h when it strikes a horizontal coiled spring and neat cdec/3+qp86 7tq is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.1m8su btzu; 0 con2gchb)i z7r/(nt 1n00-kg book from the ground so it is 2.20 m above the ground. What is the potential energy of the book re) 0 0uszbo;rutnm7 t2g(c/znnic8h1 blative 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 climbs q7up d7f+/fomv v;u+ kri j7e(to the top of a 3300-m peaki+v7 pud 7vfeq7(jrfmk+/u; o.
(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 ah0cnv; 25.rif 5s xdgk ruler. The end of the spring is next to the 15-cm mark on. 5drfkng0h ix5c;v2 s the ruler. If a 2.5-kg mass is now attached 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 zzgc qahalm ;:b:b3 7k1c+4doat top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungl4obqzc h dmz ;1kab:g3c:7a+le. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frictionh(tpf 1bh4 cd v2stbj5*u3+jgless 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 awi8lv z+c gd/8d )8xp5qcxlffya,g, 3 frictionless 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 into gravitat1 kvw0 4lz91s: e**o w)u rp)uylhbkolional potential energy without the aid of a pole. With what minimum speed must Fran leave the groul)r0*pkwb1:4l) *hsuoz v1ywo9 ekul nd 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 vertically upw1(fvf apwns ;c *;98j1la cycyard from the top of a platform with a speed of 5wysv;*8 pfl 91n(fjcca1cya ;.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 constanon 7*b c6ea3tct is 950N/m is attachc3eaot7c nb*6ed to a table and is compressed down 0.150 m. (a) What upward speed can it give 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 alongg3q5vd e tt(x la9fv9y5/,dan 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 radius is r), from what minimum hex 5fgda ,5td l9v3en yav9t(/qight h must it be released?    r

A block of mass m is attached to the end of a spring (slhjn+0ab :f.4b*kubhjfw 1/ 1wvn d2tpring stiffness constant k), Fig. 6–40. The block is given an initial displaca lw.b/h*t b j0nvu f1kb:+wjfnh142dement $x_0$ 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 bridt5t1 dhha(*inge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the * 1htd n5aith(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 shown in Fig. 6–41 is draggzohj2tmi.e5-x b5j+bg j j4 d8ed up to point 1 where it is released from rest. Assuming no friction, calculate the speed at p-zbjdht+.e5jxij b2jo54gm 8oints
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at an aw6xwymvi9 +/ sngle 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 bottom of an elevytlm fk4d6gpve :/*(-sb4f ciator 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 should 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 passcb*/ s6yl iptm: fd 4kevg4-f(engers.

  A cyclist intends to cycdo; -kp yl,vog.pd;h. * vtg+dle up a 7.8 $^{\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 95km/h in o, 4 x7d19asc/pyqigx opposite directions, collide 1s7pxa,/oy i c9gxqd4 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 reaches the bou;wd* j)qbm73ome dx7 ttom with a speed of 2.2xb e)umdo* 3mq;wd 77jm/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides down a 22xdep3 q9/ )zyg.hpf;hmg0,va $^{\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 tree 13.0 m bk8i 9a0,3nehzy v-2(*d fm.kqjdff4llv u(kabove 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 hhs0bnwu ) c(ihue2x *5qa+0cmeight of 2.0 m, and it bounces back to a height of 1.5 m0uim *w 5c)scxuhb0+a(e 2q hn.
(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 pulled across a floor with a constant h1b cxbe0+6cfy,c y.by orizontal force of 350 N. For the firsyy, b.bb1+ycexfc 6c0t 15 m the floor is frictionless, and for the next 15 m the 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 of oheo ;hgt .e:3jixt /9cn5da1 If the average force of friction is equal to one-fifth of its weight, wit/x9h35eti ehoo;jacd n gt: .1h what 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 steady upward 1y4iol8o ;y b02qg ,)tdsxd0 bqghkw2+8.0 $^{\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 attached to a very light horizontal spring (k=18 lck; )x2gspf*0N/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 the2x*cgl) sk p;f coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a hg+t)w2:d; c iz0f wwevery light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction ist: 2i0ww+c) hzge ;wfd 0.30. A force 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 shu) xahbpjdkd/)+0 )+tlsd/ic uttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the aa+h)pcsudbk0x d t)i/dj/l+ )bsence 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-sto62jihsg 1zpeg90l r7 fry window 16.0 m abog0g s62rlpj1fei7 9z hve?    s

  If a car generates 18 hp whenghb* 6 fla2 j5k1wnq xhfov6/6 traveling at a steady 88km/h what must be the average force exerted on the car due to friction and air resistance? nq/g66obhv 5jwx1ff6lahk 2*    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is the avyk1; i htj 4t*xdo fy;7sd5m)derage power delivj h4f;oy1d;d)t myt*sx 5kid7ered by the engine?$\approx$    hp

  (a) Show that one British hoi9.mg-k c21/m9vle8 t lpb olgrsepower$ \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 often expressev(/tzpg lzjw *es u1.rbw448h d 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 9j 9oo-ei z/w hhcn(w8kc:-er:*ipb bher 1150-kg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a cwz98ip-/ oh: w* ie(ejoh:n-bckbr9constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1rhscc a8f1p yhzo31a :n0.q :a.0 h? $a\times10^b$ J a =    b =   

  A shot-putter acceleknf fux xqk;iuox0:9 v* w4a80rates a 7.3-kg shot from rest to 14m/s If this motion takes 1.5 s,0uwi afkno0xk:8x uf9xq ;v4* what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute thrt8ht6u+u4y1 hxukj /j ough a height of 3.60 m. What output rating (watts) should/h uty14kj6+ h tuu8xj the pump motor have?    W

  During a workout, the football players at State U. rai9g o3ml gmax--(wvwuz5 f+.in up the stadium stairs in 66 s. The stairs are 140 mix-wzl+9fm5-g. (oiuagv3w m long and inclined at an angle of 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 cyclk f,e3lum:/agist climb 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 of 120 hp. How steep*3/s5knad-x zpqw : ou a hill can it climb at a constant speed of 75km/h if the frictional forces add up to 650 dsoq /*w x3ku5zp n-a:N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kgq.ll ci0fv34puc 6m0pxsc -f;dko ,z2 box along a level floor at a speed of 1.2m/s if the coefficient of frictionv4c-f x0zik;lf ,mqoc60upd 3slp2c. is 0.45?    hp

  A bicyclist coasts do bt)h z58 dd4x0y oomvzhb-0lh/sgu1 5wn a 7.0 $^{\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 have built “5mi/h(8km/h) bumpers”;et wn)5qac.o 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 c twq; 5.)oaneconstant of the bumper be, assuming 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 the first shelf is 10.0 cm off the e0s )wslzs r8mh6y l5ivp-g9 1ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the a0vp1-5r6i shmlgss9)8we ylzverage 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 laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous lhy4u eh 6x* 7w6f;a8xc3 kfaboong jump (Fig. 6–42) in the 1936 Olympics shows that his center fy6xxa a ;wc 3hhuobe8*67f4k of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he 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 withou , tm5x)/l qosoqo 3yn7y:p6cdt friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even c,)l q 5 :qxy6mo/ 3sdoy7tpnoat 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 37 ;e3 pw yqa/mv.tyuc,;0 m after jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater;tyqv;,pc.yu/mwe a 3 1.1 m deep, but survived with only minor injuries. 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 horizmvkpgh4d n2io tu32;1ontal cord of length L whose other end is fixed (Fin2vk1pm 4u;i t3 2godhg. 6–43).
(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-higyk-ygv;*nuqnef 4.c 1 h mountain. The climb is made in 5.0 h stf-14v kgq*ycn.neu y ;arting at an elevation of 2300 m. Calculate
(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 abw+x+wyrprt a3 )59(x ipj4wabove 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 d ab,d5z ucuojm1;;a0in California claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, e u ;;aajmd0dz oucb15,stimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and fqvkb h/b7nea,zhi swz)j v /;qw h)+;/alls vertically 81 m before striking the turbine blades. Calculatejq )7ewv ;bs/+,hbn/h iw)/hzk zq;av
(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 v6fm+8sf * * mmjwyv9bdertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and9b + swf8 mm6djy**fvm the bottom of the circular loop is 6 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 ctk187qogjicv d13vd, o h3z e6ould convert a candy bar directly into work, how high could an 82-kg man climb a lad187o3g6ohz je vv,1c3dd kiqtder 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 angle of m*u vi2 b5gro50yxod5 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 scaleaeusl mcszi.gl/0 8( 8mv6:xn, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jumxl zm:i0vs8uslcne. 8m/a (g6 p 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 grabs a rope, and swings oul vz0yun ubu*, x8d ;0hpgz7hre:si0 1t over a lake (Fig. 6–45). He releases the d0p0shbur0v ;lu1g* iyuen7 :,hzxz8rope when his velocity is 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 athlete c bv9z;)v;*fk jlbquh9 limbs a vertical distance of 5.0 m in 9.0 s. What minimum pqvh f;kzb9l;u*jb) 9v ower output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumped by revec bu3-s,v v8 weo)q+ sm(;eoovrsible turbine pumps from a low to a high reservoir. To stor eb o,;u)s(e+sw qv3ovocm8v-e 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 constant k is cut in half. What is the spring strw h7.ow,hyt z:;q+wt5 (zxw riffnessh,.rr;5hq zz:7 otw+ywx( tww constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough 37 + /jw+lbt l e,ms)roskuoopt9h048t9 $^{\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 wilsd07zh- )t ) rnklhu1zl it take to accelerate from 55km/h to 75km/h Assume th17nsk dzr h))0t-lzu he power stays the same, and neglect frictional losses.    s

  In a common test for cardiac (b x:sce.q 6c(mn r4zsfunction (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power require6n(4c.cerzsq m :(sxbd 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 a 500-kg rock vertically upward a distance of 500k g-iw2( vrg-d m, what-g (krg iw2vd- was its velocity when it left the volcano? $\approx$    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 4ku )3)z kblepm at a rate of 95kg/s (a) If this water wheel eklzb) 4u3pk )is set up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s