In what ways is the word “work” as used in everyday language the same as thattwkaqp3axhu-;m( +- t defined in physics? In what ways is it different? Givm(hut3pax ak; q-wt-+ e examples of both.

Can a centripetal for+v5abjmqkdv 1ouk8qsy;q gnp+.z-t6,f m t /;ce ever do work on an object? Explain.

Can the normal force on an object4v(csw c5iw;z ever do work? Explain.

A woman swimming upstream is not moving with respect to the shore. Is imdnw-z2rh9 9u7.*vf:e wh o ishe doing any work? If she stops sw - rzd:e7hun9.9im2hvwfi ow*imming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hinecl, 6nz) sgj/ypx48a t: Consider what happens to pn 4/68,j lae)c ygzxsthe dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard7n;q/ h6xhbp4tp te/p against a solid wall even though you are doing no wo xnq et/74/;hbppht6p rk?

You have two springs that 3kx9 zlqr+ul/h9vq3v are identical except that spring l is stiffer than spring 2 v+ llx9q q/kz39uhv3r$(k_1>k_2).$ 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 forcem;rbd4 ns8(g /byqs 9lan3er/ on a block that is free to slide on a frictl9;/ s ns8a4 yqm3(ngredbrb/ ionless surface (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 gravitatio ;9x4 c7w-1b e7gfjuup;lbcqunal potential energy change when you jump as high asu -b1xpb9; cul774e; ufqwcg j you can?

In Fig. 6–31, water balloons are tossed from the roof of a 30v 38j 8slxtp tk+qhcvmq 6e,building, all with the same speed but with different launt 6e xqs830tvv kj,clp8m3h+ qch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its 8mk*29o*xuirp9 zevr 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 causex9z ko *r8mpiuvre92* it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table dqsf 6q/o,:dj. If you compress the spring by pressing down with your hand and then releasfodqsd, j:q6 /e 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).y3y s qxp*aov;g)x*zbei5 2 +k The instructor pulls the ball back and stands against the wall with the ball against hpeb5; i)kq*yos yg vzx*2+a3xis nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy 1nnyn.3 upbvfq) me4- when water at the top of a waterfall falls to the popnun .bey fqn-41)3vm ol below?

Describe the energy transformations when a child hops around on a pogo sti);7 l ;1xwkmmad84o2xlv w fqgck.

Describe the energy transformations that take place when a skier starqqdr+j iq-:3o ts skiing down a hill, but after a tim+rd-q i3qq:oj e is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hilb(ipq u5av-m9l 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, and (b) there is frictioa-pm (q5uiv 9bn (deep snow)?

Seasoned hikers prefer to step over a fa auvxya(tp/,4iy(kn yld/,z - llen log in their path rather than stepping on top and jumping down on thy/tyxkuva,na di4 pl/(,-( z ye other side. Explain.

Two identical arrows, one with twice the speedt397,2 qew -hllis atv of the other, are fired into a bale of 92vs3t-ae7w t,lihq lhay. Assuming 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 energy, (a) ignorib)tvsi 38 7*szs8 +x1 xnajldhng friction, and (b) taking friction into account. Explain why a grandfather clock has to be 1 *)7sj8d3zts hvlx+ sn8ibxa wound up.

When a “superball” is droppedtqhqkpc/q7t1 7m.: yk, can it rebound to a height greater than its original height? .kc/kp:1h7 t7tmqqyq Explain.

Suppose you lift a suitcase from the floor to a table. The wo;(uck8 rv 4m-wubuk (yrk you do on the suitcase depends on which of the fol;u v(c(8mruku ykb 4w-lowing: (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 8 jy.rhaj 9yh0o,c o;gpower needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to climbhlw/6p ;,)nazk o nea,h j4ct/ straight uonp/wt,z,he 64ca / ;)l khanjp?

Recall from Chapter 4, Example 4–14, that you can use . cy:y g:o7xwka pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But fkog:7x. cywy: or every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational forc1, n twmw.uqb5e when a 265-kg pile driver falls 2.80 q, w bn5.1tuwmm?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work is re by0ehsausm44r xk* 1,ix:fu 6qu40ur 61e*k 4ismx,fyxb ha :suired?    J

  A 1300-N crate rests on the +ou7x.:1mksdsfo8tj w1sqt -zq *g )h floor. How much work is required to move it at constant speed (a) 4.0 m along the floor against a fqw1o.8 17oj ) zmkg+s-hq*txdss :futriction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg crate2 a9 3ddjjldvp-h np4r+ft9j , 10.3 m across a rough floo 4v39-pdlp+nt rfah2djjd ,9j r without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force acros(u.xlzp3r +lk s a floor at a rate of for 7.0 s. Find the net work done o.(+l kxzl3urpn the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table.hm;oa3b oo lcm3v5 57n3fol7 e How much wor3ocme3ob;fm n7a ohvl 55 3o7lk is required to stack them one on top of another?    J

A lever such as that / m2+g2 hgtcdat o6:hpxiyi.h.w3 g /ushown in Fig. 6-35 can be used to liff objects we might not otherwise be able to liff. Show ht/xa.o +.yp hi2 g3g/m2 hudig6:wtcthat 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 doq:d-ju bd; td2wn 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.qd j2:ubt dd;-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 ann xw 8f9iq-hn/o4r .fr acceleration of 0.10rfn i rw-h.89nq4 ox/f 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 x,t8n((xv5aw dg;vsaqx 5 cz)the distance axis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as show93y g:pr+b4 lwl kn.ibn in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m bwbp3rill:kg. 4yn9 + to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particle acts ijq0, 7m h6qy4kyocwi3n 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, with mass ofyhvza/)m +89ff30 jjlyop/ k t $5.31\times10^{-26}$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 doubl+jfp.. jn gapjhj4-2w ed, 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 (b tv 7e/r+.5njxyqb qelectron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 105kma: ji)so*cqk; /h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose stujk x3d+/uj1fring exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of dj13xj/kf u u+the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves z;ywql 0)v5xo a fielder’s glove backward 25 cm when the ball is caught. What was the average l 5;wvx0oy)qz force exerted by the ball on the glove?    N

If the speed of a car is increased by 50xwkp3h;+ +nh t%, by what factor will its minimum braking distance be increased, assuming all else is the same? Ignore the driver’s reactionkt+ wxp +3nh;h time.

  At an accident scene on a levelosfe4nw+atk/ - se8 f: road, investigators measure a car’s skid mark to be 88 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 tho: 4sat-n 8e+/ keswffe car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg nm0:+bfq q4teis pitched at By the time it reaches the plate,4 f:mn 0qtbeq+ it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock g (n/82fuq4 djzbyx02netfoxlu j/00 m o if thrown straight up by someone who does 80.0 J of work on it? 2y0etu x lmnf uo2(zdxf0j4/80j/bqnNeglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically withh2t ln70+e7nw/ ovwvh an acceleration by a single cabln wwhv/e0 7h7+ tnlo2ve. 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, os8 d; ) ulw6miz8 apshn1l;t4cf 440N/m How much must this spring be stretched to store 25 J of potential enerp 8z6ih;8a )llwds4cn1u sm;tgy?    m

  A 7.0-kg monkey swings .v; k7ylc,ehdfrom one branch to another 1.2 m higher. What is the change in potential enehlec 7d;v. yk,rgy?    J

  By how much does the gravitational potential maw)q yxsc5c84axi6 .woz4,lenergy of a 64-kg pole vaulter change if his centeryoicw4 8c)xls 6 z ,mq5wxaa.4 of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h bh d08bggj,.pbir d)b ; vez,6rt37ox when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 ebtbri8. dvb x0g;g p,73 hobr,j)zd6m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground -dm-k-dga;r,lca//cgg/ vqcso it is 2.20 m above the ground. What is the potential energy -da g rkc//- a;cgqmd/-,lcgvof 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 elevation of 1600 m and climbs to the top of a us(qe 1y.b.ek 3300-m peak. e1q(ub.eysk .
(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 ny7h1v4t20wmxy,)pf a x)sg imext to a ruler. The end of the spring is next to the 15-cm mark on the ruler. I)xg0f mhvx4)71i, yy2t pwms af a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top spexcfuta*ffg9eg.2w q e- n8 p/)ed (5.3m/s) and grabs a vine hanging vertically from a te/ 8xge fupgc-qfn9.a)w*f2 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, starting vpvtga6 n *;jlzgn-5+ 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 g0qj cxrk ,h0+jfd0/e2 a zxnxn79asv,iven a 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 kinex1x ac.*1 zg8w d+ 3ahix:jkgatic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of masdzc a+x1 *jwk:.agx gi83 1hxas 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 platfory .ax58m2 ,wwpbkv9ibm with a speed o 2, kabvm8x pi9wb5w.yf 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose spring stiffness constant- ,ch d)dm0hnt is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to ad -cnthhd ,0)m 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 show n pyqnv*.8my/n in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimumn v n.p/*ymy8q height h must it be released?    r

A block of mass m is attached to the end of a xv8clbz* ;z4 dspring (spring stiffness constant k), Fig. 6–40. The block is given l8z;cv4x b d*zan 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 bru) *f/xk t6+ xt.jeq .tdz(gfeidge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stq6 (ff*t/)xtkede.uj. txz+ giffness 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. 6–45 ;c iu-1iqaoy1 is dragged up to point 1 where it is released from rest. Assuyo-ii caqu;15 ming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/7l3w 9 zlhktg1 -8v: gsnqy*kos 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 designj367c h9dmv5; yh dnpcing a spring to be placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so 69dcd 3hjch5 v 7pynm;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 cyzwkg4h0rcd 05cle up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 95km/h in opposite directvppz cza2n(aty/22/ w* yjsc ;ions, collide head-on and come to rest. How much thermal energy is produyznja yv2(p* / ca/;t2 ws2cpzced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reab-dw:kwx ( -mknl6, miches the bottom with a speed of 2.2m/s How much thermal energy due to friction was gw ( b n6xml-:kmdw-k,ienerated in this process?    J

  A ski starts from rest and sli*hyirn :qs9.i qkz10 qdes 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 13.0 n0iasv k*/1prr2h,fim 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 heh xj6r(rrde o.w1,uz/ ight of 2.0 m, and it bounces back to a height of 1.5 m. /(erwj6rux.hz1 ,do r
(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 (cu* etuds09d across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictsc *(udd9u0e tionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed o lbat: .4oqnzy ree+*6 e*+nrbf If the average force of friction is equal to one-fifth of its weight, with what speed will it reach poin n.n+b e4yqab*l+rr: e6ez t*ot 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot ofa a oah685p 6b/vr4cdh 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 to u9m ikyd59u1pa 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 before stopping and turning back. What is thep1yki995u dum coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very ligb9j u l( xng4a13w5syrzi28m f 0lb;rwht 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 released from this position, how far beyond its equ3lrxr fwi1z4yb sna(u95bl w;2j m 0g8ilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 9uiz c *bx;xr1280 kg including pilot) that was launched horizontally airb1xu*2c xz; t 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 trv p )na;bje-l 4tfw)*o a sixth-story window 16.0 m abova peb-f t*4j);n)r vlwe?    s

  If a car generates 18 hp whs6h iki u(3 i*krqe- om,u:cu2en traveling at a steady 88km/h what must be the average force exerted on the car due to friction and air reeiik c:6si*ruk- q (mhu,o3u 2sistance?    N

  A 1400-kg sports car accelerates from k;bq:/w8vc)cf +x q wkrest to 95km/h in 7.4 s. What is the average poweqxc8)w/b: v;qk +kcwfr delivered by the engine?$\approx$    hp

  (a) Show that one British ho-+me g, g6gcjsrsepower$ \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 kc( 7b2,unqcra;nw3 kin 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 tf rll 78dq px:i,a-t fs0+6*g1 yecjccar slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveyfg*6s,ac 70j1eqf: lr8xpi+cttdl- ling at a constant 75km/h.    hp

  How much work can a 3.0-hp motos2:l7+ q 7 khahv:rebjr do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerat)5nsl7fev- bd,m4; ue; s+dkeg;ccvu es a 7.3-kg shot from rest to 14m/s If this motion takes 1.5 s, what;5edf,m) ugscs cv;bl e;eu7nv+- 4k d average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute througp7t ;lu2yk5 cpb b1l;uh a height of 3.60 m. What output rating (watts) should t 1cbpu;5;pu2yt bkll7he pump motor have?    W

  During a workout, the football players at State U. ran up the stadium staiqv33mqcj9m y/rs in 66 s. The stairs are 140 m long and inc 3 q/v9m3ycmqjlined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb a 6.u3;lovm3gw:b oul6i+qr buvw 4q6 kj*- bj5i90 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. How steep apdl 9q5hqlah/t9 2 1fx hill can it climb at a constant speed of 75km/h if the frichq h qx9p2altlf1d/95tional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to bew avz,)ht1r p9sy-/ gd able to drag a 310-kg box along a level floor at a speed of 1.2m/,)z9sdgra/whytp1 -v s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts dofzwd2/ ob.p7 gwn a 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bumperjt3k0 r;ych7vm;2zwh)h-v b zs” 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 solid wallwbt32k h0rzv- hyc;vjmz)7; h? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the grounk*t:v5gimt l/ d, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shek gm5*vtil/t:lves, 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) i81bv ,irgrjuvfcv65 ( n 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 atj5bf ir81vrgv ,(cv u6 the top of the arc?   m/s

  The block of mass m slidinw+o05sf ptv k5fwu7zk;yu)a6m,mn. zg without friction along the looped track shown in Fig. 6–39 is to rem +nkwwff5,u5ko7 z60 m.t;sy z vaupm)ain on the track 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 3703hsb:. p pbdp5 m after jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with onlp5b3d.sp p:bh y 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 fix,2 v)riq(vgyyay5i *ued (Fig.v2uqi(va yy,y r)* gi5 6–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountain. The climb is made in x;u7 clow71axfbpe /5 5.0 h starting at an elevation1 7/b xw5pux7elf; coa of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m ab7goava 9*s( gq2/ cimh q2r;hgove 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 that its lifts can move 9 pa4qk3z cv;8gft)jd47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the p tpj 93gf czq4;akv8)dower needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls36k9jw:h v-:m xqx9d + je:mlh7zklq(osq.z s vertically 81 m before striking the turbine blades. Calcv+ :qk. jsw qxqzo9sxj 6:emlh-lkhz 9 :73(mdulate
(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 loop7g(n.y o0qixf3x lq0w (Fig. 6–44), the difference in your 0iyo 3qf0 qg(7xnxw .lapparent 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 size of the loop or how fast you go through it.    mg

  (a) If the human body could convoj+y,cj 0a*fd 16pl+lmih m0nert a candy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by o++j dc0fp l*m6y, am1hi0jlo nne 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 hd :9y9i k vq m)r;ewcge/-*aisx)sk.at an 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 bat8y ;n4:kt m.uo-plxm khroom scale, the spring inside the scale compresses 0.60 mm, and it tells you your weig o:k8k;ymm txn- up4.lht 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 rope, and swings out o 9cz)c l2 4fv 2dagbh;2l/zh+cxg .ehnd.a 0vzver a lake (Fig. 6–45). Hehlzcgad z9vc. v ;nlheb f+)c4/g.xa0222hz d releases the rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs oe guh*p5n:zlhj 8t j6 9po*+zm9p;fpa vertical distance of 5.0 m in 9.0 s. What minimum power8puhe*g5hp o nz9ofp :z m l96+tj;*jp output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is kh1h6:qkdh/wyn +a.* hmru*x pumped by reversible turbihn*xw mhk *.6/uard1 :y +qhhkne 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 constant4i/3sie mvi,t1f97t vwago l( k is cut in half. What is the spring stiffness constant for each of the two749ogi twa(m fi3ei/1vvt l,s resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a c*nfbz1(tg o)v ez8 5zrough 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 3,o4ws ykx7w *i5km/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 neglect frictionawoi,*w4y xk7s l losses.    s

  In a common test for cardiac functioni-8c h7k*ideyb7; gl t (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treabe t8 *d;ly-g kcii7h7dmill 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 x0ji px,p*p 0s9xp5lmdistance of 500 m, what was its velocity when it lxpjm09 i,xs x *0lppp5eft 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 waterlh9i)sa 5 ,yst.)y,ir 0hxd nw wheel from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is its m x9yriais5h d , nh)st),lyw0.aximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s