In what ways is the word “work” as used in everyday language the same as t (3l raetiq w,p/w/hykr3n(h0hat defined in phye/wt lw3i3y(h 0 hrnq(,/apkr sics? In what ways is it different? Give examples of both.

Can a centripetal force w;2ou ofzyu9(dflh0)ever do work on an object? Explain.

Can the normal force on an object m c+wz ou-i+r 0xbusvd,o.;. never do work? Explain.

A woman swimming upstream is not moving wia4-gq1 rf yrea;eq:;e th respect to the shore. Is she doing any work? If she stops swimming and merely floats, is work do4 ;fqrg;eyq:a1 erea -ne on her?

Is the work done by kinetic friction forces always negative?r *f7i e2x9*rycsdo(ao60 gud [Hint: Consider what happens to the dishes when you pull a tablecloth out fro*giro ces 0(x2*9yfd auo67rdm under them.]

Why is it tiring to 5 1f fd0dcrsi/push hard against a solid wall even though you are doing no works fdr1 0fcd5/i?

You have two springs that are identical except that spri8fourgmg.(6k+u u ro 5ng l is stiffer than spr8 ru u5g+ .(gu6mofrkoing 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 forcf65x 91s:7n)ictngfwsr2 zypb- dak /e on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled a distanc-ws6 c7x1gsfn p9tz5di) yn :/2farbke $d$ 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 doeq5 . rblrlzas: 1**l,(dk 6 bqkytid(hs your gravitational potential energy change when you jump as h qi.l b lzdd*6br( 5,kta kys(lrq:*1high as you can?

In Fig. 6–31, water balloons are tossed from the ro)v +tne7(t 9xjb eqg1eof of a building, all with the same speed but with different launch angles. Which one has the highee 1)evgntq7+ (x9tj ebst speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h abovzh(( re ne4gc,e its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given4erhe( ,z(cg n 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 m rests upright on a table. If you compress thxmz- 9h y0445hup, kw+ptpi nfe spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservation of enkpfyth95+ 0pi z4p,h m-uw4xnergy.

A bowling ball is hung from the ceilaz+*43 kfg odping by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is f*ag3k+d oz4psupposed to release the ball without pushing it. Why?

What happens to the grav hygcl7s)ua7b, g 2)jfitational potential energy when water at the top of a wateruh7 j)bfycggl 27)s,afall falls to the pool below?

Describe the energy transformations when a cc9xg ym.:bm g,hild hops around on a pogo stick.

Describe the energy transformations that take place when a skier starts skiing j it*qn0lijc9sc65vb e 0ox 1-down a hill, but after a time is brought to rest by striki01b6ojv qiis0c5x et jn*-9clng a snowdrift.

A child on a sled (total mass m) starts fromgr 4s y5zzys3h)y5h y4 rest at the top of a hill of height h and slides down. Doey4)sh345ysz zyh5ry gs 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 fallen log in theisnbw0 :hq4ufpw7 u ix,.4 kgj*r path rather than stepping on top and x s.,qnw4wikbu ghf 0u*:7pj 4jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the other, areqm(rp1ik88 d 0q)cdu9h1jpfw fired into a bale of hay. Assuming the hay 8hqwijc(u1 m90 dd8k)p1r fq pexerts 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 penduluj,trtv5ei;yc) ljb 9 4m in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock hajijlb 9,e4t; 5)crtyv s to be wound up.

When a “superball” is dropped, can it rebound to a height grea-t k+a.0om()zb+j3 rfqfha a0.kshor ter than its original height? Expfrk. jks-a+zh 0h.0aor q)bto3m f(a+lain.

Suppose you lift a suitcase from the floor to a table.u vbxq+fvzm72kc li4-n h xk a6;/n.b8 The work you do on the suitcase depends lq kb bu8 4x-7+;vkc2 zix/na6.mnhf von 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 rathejwh34mrn+ /pbo(b q 7qr than the work.

Why is it easier to climb a mountain via a zay.7 ah 26s(yktnlt.it rm -,jigzag trail than to climb straight u(li- tk raa,y6 2h.mj 7.tysntp?

Recall from Chapter 4, E 7y zv3 ggsvmj.7u90hbxample 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 pulleh.j97gg7mv3z v u0sb yd up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pila 1ff5a mwt.9ge driver falls 2.8ft m91.ga5fwa0 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work is/w-x2rw *r5 od hv9gx*ky g(zp requiredg2 xzgokh *yd/ 9 -rvxw*p5(wr?    J

  A 1300-N crate rests on the floor. How much work ) +-v(q ijec: )n6jvg1ikdwfais required to move it at constant speed (a) 4.0 m along the floor against a friction force of 23+j g v:de)wc)fiv kn 6i(ajq1-0 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing v;elf wg; wqgsbinuv4l.-pi:.;.t. *grx d )ka 160-kg crate 10.3 m across a rough floor withl d)pfgr.v*:tx-sv4n.; iik;.wbeg q;u. glwout acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg *uf.zi5k7 )z/eekz rdis accelerated by a force across a floor at a rate of for 7.0 s. Find the net work done onei f ze7k*kr.5zzu)d / the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kgsc :b2j 0nlc-q, lie flat on a table. How much work js cncblq: 02-is required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35qj ,gw lod)qztc:87(e 5pc rvxzlz7+0 can be used to liff objects we might not othexq+ vdzel oqj7 g 7)p0(5r:tzz,8cwlc rwise 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 uw ,qq(z-wp e-j8 fhh0m down a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculathzhwq 0p 8e-f( -jwq,ue:
(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 of 01vnm4 opexa; trae.5*ve- 7 wf.10 g upward.1vof4 t.vpnwae;ree57xa * -m    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 linear and tha4o4 l3lb wow 2jm-4w,qinz 5t /pi3cnnt $d_{\mathrm{A}}=10.0$ 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 alon)y:uwuf8k b w3jr,h8l gi; wy6g the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) kjhwf l8y:bi8gur6;)3,w u wyfrom 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 particlwglw-g8 1wdkw7*5 gaf+9 u asoe 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 molecul. 6zu-vvhf h6ce, 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 whaxo y)sf4)1f 3 skl1qmzt 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 7 j.tsoh7yz o,stop an 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 to stop a 12 r)0(gjsfe4 qp50-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from acz*;d omzp 5/o 2(h -qkq*ysbb bow whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of thph b cmy- o2;5o *k/qsq*bzd(ze arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’3oh v2 nr5ndgf1p/ 6tt5v zs1(/s dvwws glove backward 25 cm when the ball is caught. What was the average forc5/ z1t swoh rv6/sp3vn1(g td dn2wfv5e exerted by the ball on the glove?    N

If the speed of a car is increaswrg.f *ip.nirtqg stt ://lz+l*u+3 z ed by 50%, by what factor will its minimum braking distance be increased, assuming all else is the same? Ignore the driver’s reac il fi :*.pzwtg3+rlttq/* nz.u s/+rgtion time.

  At an accident scene on a level road, investigators measure a )) biyp ;fs3qjcar’s skid mark to be pq;jf ) 3s)byi88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass o /g8uwimmq8 2cf 0.25 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, if the distance between t8 mu8i/qcmgw2he plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown d+8rh/v 0tc dcp9h c:xstraight up by someone who does 80.0 J of work o:ptxrh+c 0 d9/ c8hcdvn it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration b kxkxx a- c(l/3 n.+fik(i:ihcy a single cabkc(x:k3ix- ixc +lh( n f/kia.le. 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 440N/m How +ahaiotu -vgf ;q. x0,much must this spring be stretched to stoah xoa.,t+0qf;g -v iure 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. xo y-k;,f11e,tb7xt n ;wbyrrWhat is the change in potential enern,xeot7 1b b ;rkftxy-r1;y, wgy?    J

  By how much does thejw97;gxlx 6 6cbs jgb5hns ;;h gravitational potential energy of a 64-kg pole vaulter change if his center of mass rises abs; g6lwj5n bgxcj 9x shb6h7;;out 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h whe5548d: ypsvzz,9x gb; hwgheu n it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness conss5;h9vud, hp 8zggy4zw:ebx5 tant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground s4qmpcx(o ekpp)1da*4o it is 2.20 m above the ground. What is the potential energy 1m4dc)*op a4e xqppk(of the book relative 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 edk; p/bkh1 k y7+mdo,nf qkilu /t-k kp5v82v8levation of 1600 m and climbs to the top of a 3300-m p85d+7-k;mid 1l/ pv yukv8ofk,t 2kknh/q bkpeak.
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically next to a ruler. The end of tut. 2b ja78kbmb;3p03 dvoux/yepc l:he 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, where3 2 yja:lvdx.3cb kp;07 mutp u8be/ob will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top spdx(dw k3jls2md- c20ra- gw1ceed (5.3m/s) and grabs a vine hanging vertically from a ( ldd-mxdw ac3k jcgs2-2w01r tall tree in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, startiih 2y x2e:7-d9rrebps ng from rest, slides down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove usk6: mp vp-gk/p4 ;4elbkk. oxp 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 gravitat;3qtu.,rzax+dvpbxe:a/) wxh 6u mv ;ional potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a spe u;a.qx/vvr zxhm6:w3);paet+ xu, d bed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upwzez gpnj-mp5s8n od2 81nd1 r-ard from the top of a platform with a speed of 5.0 m/s.5z-8rng2dso 81zpem1p-nnjd ($\alpha)$ 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), oinks28u2 qdem+ey0z 1 a*v/ewhose spring stiffness constant is 950N/m is attached to a table and is compressed d8a1mn /qzv 02u eoy*d+ 2esekiown 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 along the looped track shown in Fig. .psg3*6 bb*fiw n 8awx6–39. If the block is to remain on the track, even at the top of the ci 6fs pw*n g3wx.ab8ib*rcle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffness constaym 3oqep6h *5qnt k), Fig. 6–40. The block is y3e* m6p qo5qhgiven an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridgek9k5nxf8a0)p43hp5elt qtu ie1bi( d . 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 o5lxqhbp3k ( p1u i) te890 45aktedniff 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 to point 1 where it is raqamrc.zro8 q*6 m/d3eleased from rest. Assuming no friction, calculate the speed at pointsdqoaam /.zmq* c8rr 63
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at a60dd ke2,e-g3vpcb+s x5tw xjn 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 beb d+trtwm*7 k+mi7 *jr placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the7jr+ dmk*im7*+wtbr t 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 passengers.

  A cyclist intends to cycle up a ifk ylvs/3w z+r232lwn;f9 kca7r tt +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 9qt. qb 8x3xmctraveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this collision9qb. tc3xm8x q? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m highd1i *n;)lqhw t3k :hqxhh d+hk6z9(z p and reaches the bottom with a speed of 2.2;l6hhq hz(wdtxdi1kh :k 9 *zhn3p+)qm/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides down a*o9fh qwrcc hj0( kb83 hw 06/5mvuset ggf92y 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 drls49ct t oqai3a- + rg/x)u;ycopped from a tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back xglgp rw 2.;g1 uq1niv7. 0xkjto a height of 1.5 m. .2w1n k.xjrlip 07x v gugg1q;
(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 6 dauv*ywc**g 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 sp cwuyv*a*d 6*geed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a spee2 ljccxd9 id7z 5xr3 y8q1bv1md of If the average fo85v 3did9 1 qcbjz1cy27 mxrxlrce of friction is equal to 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 of a steady upward3;j hn7rollmw *pmce,n 9b5r 2 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 to a very light horizontal spring ryc-upo1bzl4x8r 3xxz -al /; (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and x83l uo; rxab-/-zlxz crp1y 4released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal spring, Figi9 mw )ftg(iz :f7;njz. 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 released from this positioj znm9ft;7ziw: i) gf(n, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass ourtt/7ss.nio7he t (7jf(/j rf 980 kg including pilot) that was launched horizontallyr /fstehin7js/t7t7jru.o ( ( 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 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 d19b70mx 8ugcxfs * bmto a sixth-story window 16.0 m above*u0 gx1cb7b fxs8md9 m?    s

  If a car generates 18 hp when traveling at a steady 88km/h whatkjvx 0zi d)6f: must be the average force exerted on the car du6 zif0x)j:kv de to friction and air resistance?    N

  A 1400-kg sports car 8ig rr298 ugk tqr)q3)nl-bxu accelerates from rest to 95km/h in 7.4 s. What is the average power deli q9 r2)) xburn3ru itgl8k-qg8vered by the engine?$\approx$    hp

  (a) Show that one British horsepow+8 kg0 s1qdlicer$ \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 ofte)d;, adqj9yrmn expressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 65km/tedfc7 8mle*s ,dk; 75mrs- uhh 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 consta75,ec*f;dlr mdetmu ss8-7h knt 75km/h.    hp

  How much work can a 3.vkki c(-xy /8j0-hp motor 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 this motion takdzdq/w *js;cb8 (v/h0h7khw8mmet 0nes 1.5 s, what average power was mdh0wv (hh8b z7m8eq/ *cjsw 0/d;n tkdeveloped?$\approx$    W

  A pump is to lift 18.0 kg of water p5l2 )2km:y3 vtzd g 2vgtdh7xfer minute through a height of 3.60 m. What output rating (watts) shotv : 23ly2t gv 7f)mkg5hz2ddxuld the pump motor have?    W

  During a workout, the footbar.h. .jo.5x0ad 7 mqk*bcoo wwll players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined at an angm*.ohwd0bc.rq57 aox.owj .kle 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 p9;pu ynw,7 3mdqqi0 q6.0 $^{\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. Hof; iga78oe-hl w steep a hill can it climb at 7-ilhog;ea8fa constant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor havwvhy 40;26ynx daex ,be to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of frictio,hvb w6y2an xy d;4xe0n is 0.45?    hp

  A bicyclist coasts down a 7.ly63 8h1eiw kdu h5ux(4e3 lcv0 $^{\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(8k31drntjmx -c1n6m l(im/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a soli nc3-dmrlnx1tm6j i1 (d wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off thkwttvxx8.m /1 e 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 wivx mw1 k.8/ttxth 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 Owensf4v*)rw53 tgsliyvzy/ zom(d ,l8ua)’s famous long jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at s5adlr(f) m ,v /yto wgl*34izy8uzv)the top of the arc?   m/s

  The block of mass m sliding without friction along the looped track shownv. xwt7i 0gpr: in Fig. 6–39 is to remain on the track at all times, even at the ver pxit7g .vw:0ry 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 jumpingi08 vcjvrg(f3d2l.g.yvka -f from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s macifj r-g3v(.v lga 8.0yvf2kdss 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 oy7ae518qyz1 ahrlo* 7y t4zkf f length L whose other end is fixed (Fig. 6–yzqfh84zeyl 1 o 7yaa*57t1r k43).
(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 mountm-r kv 2r ra5m8c9wdt/ain. The climb is made in 5.0 h starting at an el5wv2 9-t arc/km8dmrrevation 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 break8/kz fn) qyca/(l*oqerv *u y-b-tq c/s when a 920-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 California claims thaswd7 1zi* x94wma y)urt its lifts can move 47,000 people per hour. Ifxww*s mr a1 9d4iuy)z7 the average lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls s;plmd x(rapp 4643tbn (zct* vertically 81 m before striki4;ps*bz6r dp 3lx(tam( 4cntpng 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 ,0c 3dxqyiz o9m)6(4*c;dvsw4n8xp kcllo ho a circular 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 frictp( 90o6 s4mhydkn3) cc,oi8 l vl z;o*4cxwdqxion. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convel4 3 bw-glim45w k)me ai16qourt a candy bar directly into work, how high could an 82-kg man climb a ladder if i ki 64mo e) 3mwwaqg4ubll1-5he 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 ang jr b51g) v. 6;3izhvry-cojb 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 compresses 0. *3lpad2tqo .h60 mm, and it tells you your weight is 710 N. Now if youothd3.2 lp*a q 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 8oc.v3.lscug msbh,1a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his velocity is b81oc.cvg, hm3 ss.ul 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 di5fao j,z3 o(m3 wvqjt3stance of 5.0 m in 9.0 s. What minimum power output was uso,j3 a33w5( q mjfzvoted to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water i4/;cekwks ojxwdby/t;o ct-r(e c:/4s pumped by reversible tubs(otw-/ jok:c;k4wr ;4d /cxecet y/rbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cuyv9 9jd -jhb (*sro6iqt in half. What is the spring stiffnesssvr-9h d*( io6yb9jj q constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8( csno6ups .t+wpw4 ))*oc zoq.0 m up a 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 accelerate from 35km/h to 55km/ro)2ynrh2n :hq+f.ch 2gpe8lh in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect fri+hq 2gre8nf:hl2) yorh n.pc2ctional losses.    s

  In a common test for cardiac function (the “stress test”), the4u:fxewse 9e5 patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the :5efs4ewxeu 9 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 5el ;xr20nmn+euz6g1 o00-kg rock vertically upward a distance of 500 m, what was its velne 2lzn r0e;x +g16muoocity 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 og :q; 7pdhx,r/f9gclr f 2.0 m at a rate of 95kg/s (a) If this wat9:ggxf cl7,qrdr; /h per 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