In what ways is the worfqe4b ;gy 7/v;2e1 xfpjatep/7 4pudtd “work” as used in everyday language the same as that defined in ;yee f2qgt7/apv4xt1p djb;fe /pu 47physics? In what ways is it different? Give examples of both.

Can a centripetal force ever do work on an object? Ex0 qm.9ycgg( hre 82akgplain.

Can the normal force on a h,9w kbd,avn1n object ever do work? Explain.

A woman swimming upstream is not moving with respect to the shore. Is she doin4 sk-8j oekk5zg any work? If she stops swimmingke-j oszk84k5 and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Cpm; sirolpaa n)80 d76onsider what happens to the p 7r;8dslamp 06)inoa dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you arkl wgw,iu.5;6l2:xmx)a2 kldm b amv)f ia 5a5e doing no wo:5dl5w,a amlv) ) k5u 2aaixkfm m.i;xl26wgb rk?

You have two springs that are identical except that spring l is stiffer ,izq9-r40cu* j 9zcy*7 l23r pnk+habklzvqlthan spring 2 0zj nq2la7 4h,*9 k3zvzprcu*blq r +yckil9- $(k_1>k_2).$ 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 o lxm eurj lt t-)5fj;a:uhwjr*wp08:4n a block that is free to slide on a frictionless surface (Fig.6-30). The block p*mwwh:8lf0l: t )ru5;e4jatjj- rxu 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 potential enku d8/c flgrl xau ; hg-6w1n)w1;co/qergy change when you jump 1ld u;w 6gn rcw-c/ohqk1 )f; u8/axlgas high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a p8; wdsv*;;:srk+:pv p o. ,rcdczphmbuilding, all with the same speed but with different launch angles. Which one has the hig,;r.m pch: kr o*zpsv+s8;vd: cp;d pwhest speed on impact? Ignore air resistance.

A pendulum is launched from am6bemrrw2x33 db d :3 e3cxt iw26kd)a point that is a height h above its lowest 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 cause it to swing the largest angle frrcdrk i 3w b33 b)t:ex662dxmwm e23adom the equilibrium position? Explain.

A coil spring of mass m rests upright on a table.w 9k4vpi )qm1,r3m ef/f on-ow If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of cons1mm , n)-o4 rwep/f9fiwov 3qkervation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The in f (un5-6c3am:h essbpstructor pulls 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 witho- (hs63p: efsam bnuc5ut pushing it. Why?

What happens to the gravitational potential energy whe1v+ikh;9egof*c kvb6p4 nq0up +3: rn:kbo m yn water at the top of a waterfall fab:un36o *;v +4yp :hqm+pg1oc kfn90eb krkivlls to the pool below?

Describe the energy transformations when a child hop;; , /n:oy (rsgd dm2i,zejhmbs around on a pogo stick.

Describe the energy transformations that take place when a skier starts skiing dq ))gx,rcg z0rown a hill, but after a time is brought to rest 0 rzx))gqgc r,by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the :, c8+9njnywvu)qm vwtop 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 there is no friction, q9wn 8+: nwcjvvym, u)and (b) there is friction (deep snow)?

Seasoned hikers prefer to )vo;pk)(efl hm )1maovkmv+ :ud2sg6step over a fallen log in their path rather than stepping on top and jumping down a ohvs1)lu odkm) g 2m(mvp+v;6fk):e on the other side. Explain.

Two identical arrows, one with twice the speed of the other, are fire.4(cp io(r gdtd into a bale of hay. Assuc. p 4tgio(rd(ming the 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 en97:n y/bp/pl uiftq v))xs 1nnergy, (a) ignoring friction, and (b) taking friction into account. Explain why a grand/tn/9xn b 1pflsqni)p)y v:u7father clock has to be wound up.

When a “superball” is dropped, can it rebounwkm 0 b5 fs0(/a5muleid to a height greater than its original height? Explain.5 eb/k(m0u i0sl 5wmfa

Suppose you lift a suitcase from the floor to a table. The work you do im1z3ao+j mi: on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the ti1o :3zjmimia +me it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the popmd su. -nf3m2wer needed rather than the work.

Why is it easier to climb a mountain via gm2yke, x0f7ka zigzag trail than to climb straight uk gmf exk027,yp?

Recall from Chapter 4, Example 4–14, that you can use a pulley and rope3b7 niwf 0n2 gussw:6ds to decrease the force needed to raisenbi06f w:su7nd32 gs w a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done bh/4 0wak3vpqqi 0d*k ey the gravitational force when a 265-kg pile driver falls 2.80 m? id0h*3qvwepq04k a /k    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. Hy dfl7ro 0n+gq 8u0:ifow much work is re7u:dr0fq 08gnfloy i+ quired?    J

  A 1300-N crate rests on the floor. How much work is required to moves6m3pc9jkjyb r4 t.. v9wm1n y it at constant spesnrp .m6jm.9y4wyj19kt3cv bed (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 the movers dqpuqza 0 u86q;o (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without accele6qa8 uz 0quqp;ration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a w7ht-snp-( jbmqek o* djmw 7. (;hvzyp 645mcrate of for 7.0 s. Find the net work done on the bo -pd*.q(ymkh(w jh 47vpmosczm ;6n57-jetbwx.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. Ho h8t2ufjj ;+evw much work is required to stack th feju2vjh;t+8 em one on top of another?    J

A lever such as thatyk0u wux*2y2uz.lt)e 3 ayfh, shown in Fig. 6-35 can be used to liff objects we might not ot, f*3yuyhkltauw2 u. ez0xy)2herwise be able to liff. 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 m down a 28° incline and is kept from accelerating 0ele ; 87ni ksx*wd84clyqx0ul() ys tby a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is iyl; x)(txwel4e8s q0*k80cn7yl ud s 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 heli7vg(9 i4y:x ykh oj/mb4l * znn1v1xgbcopter of mass M an acceleration of 0.10 g upwarb : oi 74jnxnzy lkgy4vb19(xhg *m/v1d.    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 d7qo z- 5edcayvkg +,d+istance 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, varq kbxi x1fmaz+m4s, mei*:;q.ies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m to x = bi4 m.+eqa *x,1mqx :smkz ;if10 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 -. 5o h-lqux hwguyyj 2 -9wkr7(qza*lthe $+x$ 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, with mass o +,pv atcr;h-/1kq v4kh6zd jbf $5.31\times10^{-26}$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 factor has its speed increasedd- bx pv65k4kz? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop zixg39s s*yz5an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 70q9hn b49 ysi juukaool3-1cto stop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an av-nxwm 91hfozp 1swq18erage force of 110 N on th1pwxzofwq9sn1m8-h 1 e 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 32m/s moves a fielder’s glove backward 25 5so1mmxg0g-j cm when the ball is caught. What was the average force exerted by the ball on thejg1xs 0mmg5o - glove?    N

If the speed of a car is increasedj5rcif2q4,0ebav9(e yds 9 ul by 50%, by what factor will its minimum braking distance be increased, assuming all else is ci40sae95u2 9dqb( jfvry el,the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s exw9c q+g,5scl u3 g0uskid mark to be 88 m long. The accident o9ew ccg5u gxs3u,0 lq+ccurred 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 pitched at By the8.iny b-r )x3d l4bvon(acdf, 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 thedr df,(x a8y nlbbi)v.c4- no3 plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thro)sm8:i aujg(gv hqn0j)b o5w-wn straight up by someone who does 80.0 J of work on it? Neglect air resista08 vm )( hq)jnabwj5-g ou:sgince.    m

  A 285-kg load is lifted 22.opvranq., fbt* dpjwy5k 8 w1b.46r7 p0 m vertically with an acceleration by a single cablkw bt,v.75pr1onf*4y baw8r pp. dj 6qe. Determine
(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 4h81 mzdbfq6n(w s) thsz sf6(640N/m How much must this spring be stretched to store 25 J of potential energy? fhz8s hw(b)z6mnd qstf 616s(    m

  A 7.0-kg monkey swings from one branchsy t)e16kr yh2 to another 1.2 m higher. What is the change 2 )keryst6hy1 in potential energy?    J

  By how much does the gravitational potential energy olfrrii7 1v-x:f a 64-kg pole vaulter change if his center of mass rises abol: fi-xr1 vi7rut 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 kejr-oy3 wpr*( m/h when it strikes a horizontal coiled s3we*-rjop r y(pring and 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 2.10-kgfb(f.r 86 kyj5eja6 zx book from the ground so it is 2.20 m above the ground. What is the potential energy of the book r bfe arfyjj6zk685x. (elative 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 78xe i /.jy4ox;6n 1mejbibnlx0a2 v*m gxwe,of 1600 m and climbs to the top of a 3300-m peaj7a6vm8;b0oxny1nji l xx x2 w/ b*me,ei.e4gk.
(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 ;v dp nbm;5/r4*fv zp(o7sucn end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spos( 7vp4nz dm /up f*5;bn;vrcring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top spe/hb bfu u;-930fadnt yed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she udu -0hfbyab3 9;t/nf 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 frictionless 3sk6-ig4vpz tr :-5xmxhj7qh8y y/ 6r j5.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given gpn4 :x,jis 9em,wrgn ,yme/ ; v;zm2ya shove up a 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 gravitational jp;vfy6,r. 8 siaqy(wpotential energy without the aid of a pole. With what minimum speed must Fran leave the ground ivpa.8 frwy6,yq( sij;n 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 upward from the top of a x3qmh8ec euefd4j 4bh; 1dt+dd+gu-6platform with a speed of 5.0 m/;+4uq1eed4e+68- h hbtdg dju x3cm dfs. ($\alpha)$ 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 is lidql, zp-ob;,z(e 9e950N/m is attached to-dez,p9iz;(,llbe o q 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 frictionw)oi it-9fd4h 7 d0ffwq5t 6ct along 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 rfdi7of t-d50h fqwtw94c)6ti ), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (sprw0w+ cvr 1w5f0frww ;ring stiffness constant k), Fig. 6–40. The block is given an initial dispfr;r w0w5 w1rc0+fv wwlacement $x_0$ 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. She is tied to a bungee cord whose ia f-,larmh)i,eon 6u+/ qm4u unstretched length is 12 m, and falls a total of 31 m. (a) Calcmuiu4a+r-lq/,afi h)o,m 6 enulate 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 shown in Fig. 6–41 is dragged up tje, *fenxpaiak ; .:;t2aele)o point 1 where it is released from rest. Assuming no friction, cj:2iepxtnlka ),aee;*.; ea f alculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is throw/at4g- yv58lty+7m b 0r *0tkndqogqpn with a speed of 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 bottom of an elevh5jkx ncad l;j* vt4lh6:cc9 0ator 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 resxda:5;vkcn*hlt 4j6 9h 0jc lct. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up a 7.r6 ubgkwla zr2:z1ch*9r k:un u43 bg+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 nqq1i t6k/ihhp01xyhi d/ u8tf .sw76of mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. Hh/w /iqu.hftt 6i8h17kxn6y dqp 10i sow 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 redhr:7jf(9 n ghaches the bottom with a speed of 29g hh(7 nfd:rj.2m/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from rei) x e q8(gpr/g4cznin8l5zo) st and slides 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 tree 13 xt(s / x 4ts+lu2rra/b51bucmb) p2pg.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, and it bounces back to a heigh* p6l cq0f/da-a,. swvdwm g2xt of 1.5 m.am2 ,x6l. /qwac-fvdg* dwsp0
(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 constand ch77dk/f8c tt horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of fric8cd/ 7dkhf t7ction 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 qowbdiqk( 90dju-g2 vm u(5 *y If the average force of friction is equal to one-fifth of its weight, with what speed will it reacd(y *q0( i9uj dm -5guv2bqkwoh point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady upward 18.0ha 57y0wvc ar( $^{\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 horispd for:akcq4/vwn5- .q.f*1vglt 4 kzontal spring (k=180N/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 4o qrg ts/p.:5wvf* 1kl cqk.n4v afd-back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a vi -dw5mks4(nvery light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the sprin4d sv5i-mw(nkg 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 used a “glider” (m fe,)0 w )hahjix.plw3ass 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 be)a) p3,.l ewwhix0h fjen 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 u02 cdc*w:pkt 9rx-tcwindow 16.wku x 0-cct2:drp9 t*c0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be the a *f3twhij35tl verage force exerted on the car due to friction anw*t3lh f3i tj5d air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is the avera a4rnkwk0h q-6 clnj5+ge power de+h 4nqn6jk5clk r-a0wlivered by the engine?$\approx$    hp

  (a) Show that one British hv9zso33 2d9gcg8a0is wc g+wjorsepower$ \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 expressed in the form oran*rf(xp 08n f “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 au)p/7,trtsospkl6) j bout 6.0 s on the level when it is in neutral. Approximately what power (wat 6ssj,kpt))ptuor l/7ts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp ul-+a g,5ewo fmotor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14mf5c; l6hh8j bdeppn i5pj12r -/s If this motion takes 1.5 s, what averab epd cjp2il5 r;hfh65pnj 81-ge power was developed?$\approx$    W

  A pump is to lift 18.0 kg of watevg1ob,z iab qjsx76mi2v7,3 uc0 wdm0r per minute through a height of 3.60 m. What output rating (watts) should the pump motor have? uix vi002,7ga3 cdbvz6wo,s m1jbm q7   W

  During a workout, the football players at State U. ran u 4oq.8n/oqhvu p the stadium stairs in 66 s. The stairs are 140 m long and inclined h n8u o/qq.ov4at 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 cyclist climb a 6.us6/ j2 gq:xr.u b5aie0 $^{\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.bzhlt3iftz c370 z+o 120 hp. How steep a hill can it climb at a constant speed of 7z. fo7 cl3b3zhz0+tti5km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg boxj,w *j0gq7-r gcue6fx along a level floor at a speedg7ur -xjq6,* ej 0wfgc of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a*u3kn8 pnrqt2lzz;y 2 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 n*ph0 rk: pfq7-uum6j built “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km :6rqkh7-*pufnpj um0 /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, 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 10.3hw rb(px( w)q0 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 oh(wb3) (pq xwrf 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 famo fq1q 6hib b2fa+bdpj5 +-zzg4us long jump (Fig. 6–42) in the 1936 Olympics shows that his center of mas+ fg-h2q zpbfai+zqb1d 46j5 bs 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 without friction a79ufak owk,)pxlq1i2squ,m1long the looped track shown in Fig. 6–39 is to remain on the traqk , p1lfuuk )w,qoxm92asi7 1ck at all 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 aiwa 3xk.ms ;xazm(8-y jrcraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with onk8 jx-z(3myxmas; w .aly 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 horizontal cord of length L whose other end is fixed 5+rcc;ebc9p 9hao lr1 (Fig. 1;aol+rcc 5 9r9hpbce6–43).
(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 climbs3.2jgmp2(3s df v-i/njysao 6vy-zae to the top of a 3700-m-high mountain. The climb is made in 5.0 h starting atpsov ge3.s-zj2 (d-fn/a 32m iyvyaj6 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 920ok (u :aszbtm -eem1gzz0f2;+yd q*i8-kg elevator is 28 m above 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 Californism2kn bzoz7ud+; 4 yb2a claims that its lifts can move 47,000 people mdzuz4yb 7 onbk ;22s+per 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 damh 1nn ( 8arqpnc72by7b at the rate of 650kg/s and falls vertically 81 m before striking 2 87pnn( cq7abbrnhy1 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 qiruofw q1-76. 6–44), the difference in your apparent weight at the top of the circular loop and 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 siiuq1f r7 -qw6oze of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly into w2)j7ov;*tlbwfuo y+0 rub8 m dork, how high could an 82 t)d*urb y+7j0vlbm8f ow ;ou2-kg man 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 7z.lfgc 1i4*/g hsgk5gb q( gvp(t wh8an upward angle 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 scale comprm xj w *o..w hlgvpxhka/p8)z4xp k/+(esses 0.60 mm, and it tells you your x/8.xph4z/pw)aj*h l(+xp go m wk .vkweight is 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 grabs a ropem xnzt-794yf e, and swings out over a lake (Fig. 6–45). He releases the rope when his velo49mnz t7fxy e-city 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 climbs a vertical dis ac2ymrn :80xmtance of 5.0 m in 9.0 s. What minimum power output was used to accomplish this0ax:ynr cm8m2 feat?    W

  Some electric-power companies use wak2:.l uux8nb1i) klbs ter to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-M2x1.uuk8ib:n lb sl)kW ($120\times10^{6}$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 halfrxp8yium:;2zx,w-9 tmkn 7ka. What is the spring stiffness constant for each of thex; kamim9nt -82yu7p, :wkzxr two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough 37 n tjr4ifv/43 z$^{\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 willg1i8(fy lx c0-4mlh la gilg99 it take to accelerate from 55km/h to 75km/h Assume9ga10lx i-gi9 yh8l(g lcmfl4 the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient walka;ygdv:r 2 gg9s on an inclined treadmill (Fig.2g gyd9v a;r:g 6–46). Estimate the power required 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 50ds;oi4) -t 1htw yxow20-kg rock vertically upward a distance of 500 m, what was iw)d oot h-241yxwst;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 axua7wqa, n6 b 73v-gspls((rk0obp7k height of 2.0 m at a rate of 95kg/s (a) If this bxok3 (l 77qw,7 r(upsg n-p6aaskv b0water wheel 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