In what ways is the word “work” as usejk.e m bih-4+arhf 63gd in everyday language the same as that defined in physics? In what ways is it different? Give examples of g r4k.e6bmha+j 3f -hiboth.

Can a centripetal force ever do work 9l z.+68igd dn t6run2,:dbaq kvlkm(on an object? Explain.

Can the normal force on an object ever do work? Explain. bqe jw8 :cu77eb1x;jm

A woman swimming upstream is not moving with respect to the shore. Is sbzl+z kn :1:1wwb:e oohe doing any work? If she stops swimming and merely floats, is wo:l:w:e b b+ko 11wnzozrk done on her?

Is the work done by kins.2 bh8h2zg. cg-f txdetic friction forces always negative? [Hint: Consider what.8g-csx2 db2. zfghth happens to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a so 6 2 dfpbqs1lfypqy,,;lid wall even though you are doing no worsby,fqqp26p ;d1,fly k?

You have two springs mlzoy-z0 3 .j3llm:zmp0vqy .that are identical except that spring l is stiffer than spri 00lmy- ozzy: 3vmzql.ml3 jp.ng 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 forceaenu k272 8hca on a block that is free to slide on a frictionless sur7a nc ae2huk28face (Fig.6-30). The block 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 oxsu26pqo (n6.v r0fsenergy change when you jump as hig20v(xouor6n. ps sf6q h as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, auphn 1qhbb6t. p*2ee )ll with the same speed but with different launch angles. Which one has the highest speed on impepe q.1bu6hpt2)nh *bact? Ignore air resistance.

A pendulum is launch1x1k;cnmxlr ( cqcjrj;f:hmhz:52l* r s /y n,ed from a point that is a height h above its lowest point in two different wk1zm5/llr, hh:fcrx :mjjx*1 ; cqyc2(snr;nays (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 equilibrium position? Explain.

A coil spring of mass m6y ndlv0 c36kn rests upright on a table. If you compress the spring by pressic6lk6n dyv 0n3ng 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 wire (Fig. 6–33). Th) v-zzwpfv/0j2 xoo*0m2m ifj e instructor 0 ozv*piw2/- v jm mfox)2zj0fpulls 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 gravm.wu;sk+4n, z -0. gyyyspczquuo s; *itational potential energy when water at the top of a waterfall falls to the pool bekcgpoy, .+yssm s.u0q - ;;y*unwu4zzlow?

Describe the energy transformations when a child hops around on a pogo stick(gg 7 :) hqn s v05/vbzcy*9j*fhbefld.

Describe the energy transformations that l6;zuxsnan m*1dmr 1( j:jj/;3axc so take place when a skier starts skiing down a hill, but after a time is brougho1nmcaz x:j;ud3/xjjnm(r1 6a; s*sl t to rest by striking a snowdrift.

A child on a sled (totaln 7y73cvmj0(nc 8y wdqkxom-6 mass 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 kxd(0c 6 mmcvyq773 nnow8j- yis icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefea1vxjz m58dxeqhj:1/ - lu3 idr to step over a fallen log in their path rather than steppin11lm-3 :qjvue85ajx hid d/ zxg on top and jumping down on the other side. Explain.

Two identical arrows, one with twice the sx2r( yj)0dv r4qcq eb;peed of the other, are fired 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 y()eq4; 20bdx vcjr rqslower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energ)bhrlf9qp6dx12-txycj, - 3jhj; w:vjf sod;y, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather3h,vbfdhlo )y;wj f9jp st1;x : jdxj6-rq2-c clock has to be wound up.

When a “superball” is dropped, can it rebound to a heiygm i2.ck5a:7n uhne9ght greater than its original height7.9 ce :hnugma2nk5yi ? Explain.

Suppose you lift a suitcase from the floor to a wz5y +6zsbk0 i3elzh -table. The work you do on the suitcase de yz30lzs5w6bizkh -e +pends 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, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than the w 3)wlxtb/ kz7 b*ml* rvkwzt,(ork.

Why is it easier to climb a mwlk6tjmip 5 *;x.9 b fu6hd8*y.ygahkountain via a zigzag trail than to climb straight uy;*. hf iu* mx 6ky.d9 pbka6thgl8jw5p?

Recall from Chapter 4, Exam ea dh lld2)z9)utef..ple 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 every meter the load is raised, how much rope must be pulled up9.lufelhd . edz)2) at? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pile driver fa0 g(m8azn a wgqsjo()xa(3ej ,lls 2.80 m? awaa0(mgjqj s n3oe8g ,( x()z   J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. Hrp, f4oy agz:;ow much work is req;f4go,rz :aypuired?    J

  A 1300-N crate rests on the floor. How much work is requiirll4l qq+kl(utc,i t6ii 1j(;1g c8cred to move it at constant speed (a) 4.0 m along the floor against a friction force of 230uc1 i4l lqc6tilgr(+t81lj,ik(cq ; i N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the mover ink :hl xb+n1l)27(urf g:ndas do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without rl)b(ng 2a+ d fnx:i 7u:1nhlkacceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floorgdh5tpj.c d6 i0obh ixq4 k;-2mz qx,s6p1wc( at a rate of for 7.0 s. Find the net w0k dx4;26bp(q jcg zx 5imtohp6is-1cwhd. q,ork done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a ta f;uvkon(0f, xble. How much workfx nuf(o v;k0, is required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects we mojv s -pult ti8 ng28 i)3o3y;f3;ozhoight not otherwise be able to liff. Show that the rati)oju8-th83i si3o3lof 2top n;yz; vg o 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 bi:a7qb)9+rriw- -r7oko gcdny a man who is pushing back on it parallel to the incline (Fig. 6-36). The eff waon b- q+kcrd:-ir9 igr7o)7ective 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 acceleration ofxw9rym4e0e30a 7 ew*as5 ypm8x,on xv9 b4 vbs 0.bs yw90o,b904 xa x4r w5my*vs xv8e3 nmpeae710 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 the divsga ;0z7z9w dp 1g.wlstance 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 the7s tf/z9hwj8cjm: wd 0 x axis, varies as shown in Fig. 6–37. Determine the work done by this 9 jmhj0cs fzd:/87tww 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 on a pad ly/q(j; ajmb h1(/yf 5k.txhrticle 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, w- wdyz3nq5m n u-w3je nxl5s-:ith 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 a kg)yoaymvo76 k f obaj/,97l+rrow is doubled, 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 electron v,z5lg e+9j3t dbp( ku$\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 traveling at .p u 2 qy:+zum,6llbsm105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average force of 110 N *czbem i4dbr,scjdf /8z1z c-q a++)lon the arrow over a c8i14b/ jzdslz z*mbr+ daef-+)cq, cdistance 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 cm whrw3gd(f : vla(6d v:duzzf) h,en the )fwvh :dfld 6:u( g(az3zr, dvball 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 will its minimum bru(kv. pins9 :c2as xe)aking distance be increased, assuming all else is the same? Ignor )k:p u9 ncivsa(es.x2e the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s skidlzvoqsr 37)g9c +y1uj mark to be 88 m long. The accident occurred on a rainy day, and s yj+l9o)q7v c3u1 zgrthe 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 the time it reaches the poc5ij rxq0e3 6late, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distrq6e i5xo03cjance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go (gy9tblvn2 /fh- p.nbif thrown straight up by someone who does 80.0 J of work on it? Neglect air rest /v2y.f nhbgn (lp-9bistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceler 2m- 1rfwv8k/qg+uy h,hxass5g 1 nh5jation by a single cable.hgwf1m k hn,2v+sahjgsr -/u5yq x518 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, e h0k m sob07byt4)gf4k, of 440N/m How much must this spring be stem4sb )h kbo0g4f70 tyretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m highe m53gq6k;i a4 u.pdmcer. What is the change in potential energy? pqc5me; aud4k6i .g3m   J

  By how much does the gravitational potential e eh qd7*h7fnwu e;:f;lnergy of a 64-kg pole vaulter change if his center of mass ris; *delhq: n;77u weffhes about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal su++qg, gs1h,vtlj,fr zvb9 z6q rface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What igh19b,vs,rv , +fqjqt+6 lgzzs the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person life,xbfj31 u3 jpts 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 reu j3f1,bpj3 xelative 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 elevajq 6amxz20f u8tion of 1600 m and climbs to the top of a 3300-m peak. jf 8a60 mz2xuq
(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 e 14gqww( qm2fpnd 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 spring, where will the end of the spring line up with the ruler f(2wq g1 4pqmwmarks?    cm

  Jane, looking for Tarzan k3 :p9qhp9k:re-1 bhu*bj mf*)nvrso , is running at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high crvk joh19bpkr*f bu- h)9s::3pqnm*e an she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, sliyw2/xwjqinq48 k )yw6 des 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 frictionless 2:ho 8u tx:3tab8.0$^{\circ}$ 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 tqf;5+y(kk rm jhm+y,fransformed into gravitational potential energy without the aid of a pole. With what minimum s(yf j;+mfhkryq+m 5,kpeed 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 vertically upwardl3;psl: pzbbzsdzz+l w,55v4k5. bf 8d4ap ff from the top of a platform with a spe 5:p.f bdf8vld4,+kal wpb35lfzp5;bzs4zszed of 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 6,u1u:t dh iznr0yez ew32a(bconstant is 950N/m is attached to a table and is compressed down 0.150 m. (a) Whbd e(yunw1,2u:rz6haezit 03 at 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 along the looped track shown in Fipnda6x0v j7ss v+m3we4/q7 yog. 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 heij73 0sn e vs76xa vdywmp/q4+oght h must it be released?    r

A block of mass m is attached to the end of /-:t(hzgghf nhxt: )x a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial-:x x(g:h/gt)zfht hn 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 flmwq pwb3k 0//rom a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of thl kpw//m0qwb 3e 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 draggex296tp(lkqvt ;v. j s -/y*2 kofknhvtd up to point 1 where it is released from rest. Assuming no friction, calcu9t*vj/k yn-ko(;.2vq pfth tk lsx6 2vlate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 1/ a.yrt8bhuew*y hql, 3.7jnh2 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 bottoany1 0)f vsap5m 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 ka01fya )psvn5 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 passengers.

  A cyclist intends to)nq6 x yi z-998p7cgtwyt0yzd cycle 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 ofhq( ik; brf)j7 mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced i (birk)7hjf;q n this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reach fy7wk8m0j7g nes the bottom with a speed of 2.2m/s How much thermal energy due to friction wasmw8yjf0 kng7 7 generated in this process?    J

  A ski starts from rest and slides down uk5(bfa4:hr fa 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 13.0 m above the g4br;uzwj l11 :s+ xhy)7ckhvfround.
(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 jn: 5d atax-o, qgxph8+z :9hym, and it bounces back to a height of 1.5 maq ny+g a:t h-95jzpox8dxh,: .
(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 pbmdl)cv;pl b f(g ))s)vqj5e6ulled 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 coefficient of friction is 0.30. What is the final speed of thgf)b5 bscl; edl)qv() 6 pj)mve crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 hi(q90n5.5lnkep ml tefy-f8 6ksr s1with a speed of If the average force of friction is equal t1 f9fkml e5ep .0nr5i(lq6n8tks shy -o one-fifth of its weight, with 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 ofu1vn9kac)-:p5qeb (:r*n gimrq tirh- 8g/q e a steady 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 attached l.zu.jeq r dk6 q+9ec,f 3plfl p35hu6to a very light horizontal 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 beforepz33.fep.6fe +uj6l k r9hl ,cq qld5u 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 veryp ) csqfx)9af6 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 spring 18 cm. If the spring is releasedx9apcq s6 f))f from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights fo fh*b+s+lrxic9csu3)f tp(2z *-y xbr r the space shuttle 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) Wha*l9bsbz2) sh3tfx-+pry i* (fcu+ xr ct 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 aa rc -;k 6:sbu23d,rl:rt f;yhrd8dto 315-kg piano to a sixth-story wind -oc6hrfa:y3kb; 2 udr8ds:t,l r; dtrow 16.0 m above?    s

  If a car generates 18 hp when travepo6k s8o: y 7 *of rbd/:)l48rkmakxbkling at a steady 88km/h what must be the average forcb *7 bk4klka8d8f:/m: yrx o6)sporo ke exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerxti ; uu7;g,gwhb9fz1ates from rest to 95km/h in 7.4 s. What is the average p1x; fui7g;wzu9th,g bower delivered by the engine?$\approx$    hp

  (a) Show that one British ho4q:6d 3 -k eud nlwe.n5xckg7ul(7zb c ,/lagarsepower$ \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 exprnb/ko42-3hmyh8jyr6m:k bh nessed 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 t sv:wuuf s:8nxmb+ a,.3iqu61zbvr) 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep theuqrui)v w b8u :. svz:+,1f xnstb36ma car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motorwpmor09yxv+; u.k19x-/v xcsl1sg qc do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If th kzc2(li x3kia b6r+9zis motion takes 1.5 s, what avera ar9k 26ilik3zx(bzc+ge power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a *seoavcz(z 9gft 3j/6height of 3.60 m. What output rating (watts) svzc je9 f*st(3z/o6g ahould the pump motor have?    W

  During a workout, the football players at State U. ral5v)9h qi +lub5il o5vn up the stadium stairs in 66 s. The stairs are 140 m long and inclined at an angle oi55u9qb) l+lhvi5 ovlf 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 cxmvz5t - tkwv5 qo 0ap7;o6)hxlimb 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 o) g1aa*uog,-h rffh;o utput of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forces add up to 650 Noo a-,*h gh)ur;1fgf a?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg b io0ll+ip i1i:ox along a level floor at a speedpioii0 +:il1l of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.0s.-m k0ao8rmu $^{\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/hy j*f)bfw xc9t*lh;5 m(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*l mwt xhy;j) 9fb*cf5 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 ise/ce epw-cs l/ k:)5bz 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previousw)plcz be-/ecs5 ke /: 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 laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Olympics showwb8t )nissdt.8 34mb 4m(x pgks that his center of mass rose 1.1 ps)mmdbkx.b8 48tg3wn ts(i4m 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 along the looped trackk 1jke3b-vxu- shown in Fig. 6–39 is to remain on the track at all times, even atvju3k1 bx-k-e 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 his para9zh1:i ltzog7u h rl//chute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass wau7:1l to 9rhzz g/il/hs 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 cordqp j3zd9)lcm 4gsm-h0 of length L whose other end is fixed (Fig. mh) s4p-dg3 cjqm0l9z6–43).
(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-high mountain.zoz)dx w;ufspx0- 8v8 pqr)j ) The climb is made in fwv s;pqzj8-ox 0))rdzx8 u)p5.0 h starting 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 v1*7bq5n olr5zpo d: yis 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 areasi:gakzj05,b(mc:4 k6 hf bnu in California claims that its lifts can move 47,000 people per hour. If the average lift carries people about g46ch5kbi :, fuzk(b:asn0jm 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rj uird otnu ;7f5+r-7.8 jb0dsn:yn vtate of 650kg/s and falls vertically 81 m before striking the turbine bnj f07ns7ti5 -unr.y;rdv:8bjtd uo+lades. 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 ci h0*n3 g/zbbu n6v)dktrcular vertical loop (Fig. 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 mb )*un t30 vdnhkb/g6zinimum 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 candyabbux. ke:ql /:in23g/ 2ujo h bar directly into work, how high could:qb o:n/u l2xgejk/2hu3 .ab i an 82-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 an upward ang uf.z0v6 6qxpule 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 insidab zyh (; zd3xz-i9tv8jvkb(6e the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the sca v8-z hzj(btid yak3 9(;zb6vxle 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 out over a lak j5.xh0 zd5qoyx f;rdxy)5x2ve (Fig. 6–45). He releases the rope when his vr )5xq v2. 055yxohxfdzx;dyjelocity 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 dista.9h zs0k 5s+.b +igqiufn0u evnce of 5.0 m in 9.0 s. What minimum power output was used to accomplish this feat? sb. isi + g0q.9fuuvn5hezk+0   W

  Some electric-power companies use water to76yje/dna;e h s 4i40 cant3sa store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy prod4;6eaayni4cjh 0nt a/3s7 dseuced 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. W cs2k mhkfwrg g3(,h 1-abo-l9hat is the spring stiffnessc--b ka1m2sk golw ,3r9(hfhg constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up ijcz7 hsm fqth7)9w 3x9gsh j *fo)n31a rough 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 acceleratefbst3v317tr; b8udv4rbg u (n from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and ne8(3rvu 3gb4brtfn7 tv1b; dsuglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the pa vr1 *+uq,rnt;md3ynl ap2-(f3zv lsotient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient whyv(u+l nso,3fad1-rvztn3 p * 2qr;ml en 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 ooto uflto a3bp 5tz,., i0d3n xe)i.mh8:dwv;f 500 m, what was its velocity when it left wndtl:x oom5vh.)epfi0dz i. ,,a3tu b 3t o8;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 wheek -d p;xdtt;g*l from a height of 2.0 m at a rate of 95kg/s (a) If ;;dt *gxtkd-p this water 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