In what ways is the worh3)xrz0a mfbsd r p,47,bffq2d “work” as used in everyday language the same as that defined in physics? In what ways ish rs7z,ffd 4bfbp0q2m3,a )rx it different? Give examples of both.

Can a centripetal force ever d4cqcu 7fnq j glg,2at4(xf w(8o work on an object? Explain.

Can the normal force on an objects)u s/vk7akbm*0oo 1k ever do work? Explain.

A woman swimming upstream is not moving with rejp;ohb; b9xu 4spect to the shore. Is she doing any work? If she stops swimming and merely floabp x4ou;b; jh9ts, is work done on her?

Is the work done by kinetic friction forces always negativeq fq)m 3hwc7f/tv 5ggcgfouv8 / o1 j/hx63ej7? [Hint: Consider what hap7h3o5387 jg/fq6 qg1mhvxgf/cu /ofv e tj)wcpens to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even twhlkf*57 2qbmhough you are doing no 52mlf *whk7bqwork?

You have two springs that are identical except that spring l is stiffer px e-. e3)usqithan spring 2epq.is-e u 3x) $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that jgfa/7 d1;4b ef5hm +qsk*vt lis free to slide on a frictionless surface (Fig.6-30). T dstkb41f7ve f *+ ah;mj5l/gqhe 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 duwo:*, p qx*wgda 0nw9oes your gravitational potential energy change when you jump as hiuqd0* wnxww:o9gap,*gh as you can?

In Fig. 6–31, water balloons are tossed fox uc5vl/r()drom the roof of a building, all with the sd/clvo r5u()xame speed but with different launch 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 i fy ke:u25hrp,ts lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is gikhfpyu e 2,:r5ven 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 compressifduw:sc8 0*o.u ai9j the spring by pressing dowo: s.fi ijaudu809cw *n 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 ceshj -.wnl2vw :n5 6dryiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wallj5v n.hd s-rw6y wnl:2 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 gravisi )8dcu4gv :ttational potential energy when water at the top of a waterfall falls to the poolu )d ic4gvt8s: below?

Describe the energy tra28n, qce/c jk.zxj 2densformations when a child hops around on a pogo stick.

Describe the energy transformations that mv s10z7w*v 8 )wdaiottake place when a skier starts skiing down a hill, but after a time is brought to rest by strsdw)*o1tavw8iv 0m 7ziking a snowdrift.

A child on a sled (total mass m) starts from rest at the top t w:pw)ziv p :fhp4dsb7i,1 rz nsh4ojpp 613+of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there isp)4rfp ij+s1pw4 ,wsv36:inop hz h dbp:1t z7 friction (deep snow)?

Seasoned hikers prefer 150) mp snkiy p:pbpt (.2lxucto step over a fallen log in their path rather than stepping on top and jumping down on the )1mp tk:n x20pbpp5yu (.ils cother side. Explain.

Two identical arrows69s 8odo*mu1+cv a0aoa1l fm v, one with twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrowafdaom 809vsa+ u1lc61 m oov* will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy, (a7lzlyh8;wj; h ) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has to be wolh8 7;;hlywj zund up.

When a “superball” is dropped, can it rebound to a height greater than its orig* n/j2l4v txfnh52znk inal heigh k22*j n/lxvhfn5znt4t? Explain.

Suppose you lift a suitcase from the floor to a table. The workc0t qdlm--a sst (gu05 you do on the suitca sml0 ct( gs5-tdauq-0se depends 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 pows: h500gvb ugj(*ffvso:9 tu wer needed rather than the work.

Why is it easier to clim- u z4ul;+r2nphb4(b hauokc.b a mountain via a zigzag trail than to climb straight up?-k hc+ub a4u2zrho4(bp. ;nlu

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropro drcfaz2bkdu) *::8es to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is rairfc z*a: bk2dr:8 o)udsed, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the grxk lm8mi g;n;( -z)h+mn,hkwf avitational force when a 265-kg pile driver falls 2.80 n8+ihm-xm,kh);k; (wzl g nfmm?    J

  A 65.0-kg firefighter climbs agc9(, q qqmz9e flight of stairs 20.0 m high. How much work is requircqme( q99qzg, ed?    J

  A 1300-N crate rests on the floor. How much work is r-+,6 9yn iecs 9bthfopequired to move it at constanpf bto-+ ihsyn6c99,et speed (a) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg crate 10.3h w7oj kz no9/kke+;fdaprns/2 k8c+ 9 m across a rougrsz ofo nc/ jhkdnk9p;2ke a7w+98 +/kh floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor ato; qn8r0sw, gqb* ya:y a rate of for 7.0 s. Find the net work done on the box.:bor q8s, *nqg wya0;y   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. How muchsr,2 cb6;sn jw work is r cn,sw2r sbj;6equired to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used tknj/fdzc ) r)4o liff objects we might not otherwise be able to liff. Show that the ratio of output forcen) c fdrj/)4zk, $F_{\mathrm{O}}$, 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 ib0, t0zsakg huzk kp:tn1;n. /fq:ls :s kept from accelerating by a man who is pushing back on it parallel to the incline ,;tl:kh:qpzz uns.kk1s a f0gt/n: b0(Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a heliq6 c9z;)yw 1qzg i m)/qxa4/mbcclc0ycopter of mass M an acceleration of 0.10 g u0ycc mzmq bcy)l)4/ic z/w9xqq a;16gpward.    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 -7+d ycma1c6z-ni cg6gdgobw (/ 3fajaxis 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, act5b m:d:zs:uo8 i h6i*mpn0zmding along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to mozi0 ib:8::6ds5*mmoh pn dzmuve 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 particleqk/jt jli/ ztm;ar/ .. 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 fof1 vu2g*2;ew.gcy zmolecule, 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 whalql1v)gp8t jfbrcs 48la86 * at 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 fcfg2 j:vybsn*6q ,d ;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 1250-kgcar traveling at w6 tm-xx*n.u u105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exer2;yoihu sa u6 ;4ww)ayts an average force of 110 N oa 4o i;;a)uuyw2 6ywshn the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) travelipfbc2)zis0 4+21y lfl2gh m ogng 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force ilf2+cb4op z ys0ghlfmg1 2)2 exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor wiloh b9kb r4;w.tl its minimum braking distance be increased, assuming all else is to4wb h9. k;brthe same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a card-y-;h1ghqg m’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estima g;d-y-hm 1qghted 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.sfpzha )je 6y;y4,v5d ;l5e:ksrd8o ukt9ql+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 the d5akk8,yohq)v9t ee z ;ys + p dl5jrs4lu;f6:plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown strai8b3in5 g9 rz-iz.qjwwght up by someone who does 80.0 J of work on it? Neglect air resisz. 5i-jgr8wbiw z9 q3ntance.    m

  A 285-kg load is lifted 22i* g 0*7e9he1xi roinl.0 m vertically with an acceleration by a single cable. lh7 g01i* enxr*oi9e iDetermine
(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 /8b u(h iyutv,c4 :*wo uwo+sistiffness constant, k, of 440N/m How much must this spring bws+ i u4y o8/o u(tv*cbu,i:hwe stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 me0wa6 z9js)9y+ tur+s0 kwsyc higher. What is the change in potenti0sy) w 9+wcuk6ejya+ 9ssrz0tal energy?    J

  By how much does the gravitational potential energy of a 64-kg pole vaulter cha 3*ujgm*4 jy t:rkv4mgnge if his center of mass rises about 4.0 m during the jump?rgt34*m um:y4gj j k*v    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/zi-hp1s5ejli1 7ps (v2 7ctomh when it strikes a horizontal coiled spring and is brought to reetci1 1pmpizsh (v-7 57j2solst in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the grou2rlt trr/k.6r/e fzm+nd so it is 2.20 m above the ground. What is the potential energy of the boo/lktzm/+ rerrt62 r. fk 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 clith m5xwmvkw b7it2f c*c-+8g6lqrd. : 9f4uhfmbs to the top of a 3300-m peakmlxfh .t kc-gi+m96 d4wrh8ff5vc 2b*tq: u7w .
(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 theqx lwt e 2w/0d8,)sfaro d7q-k 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 u27 fd /xwq8 q- etlso,akrd0)wp with the ruler marks?    cm

  Jane, looking for Tarzan, is8gbad- :af6:)eekw pc running at top speed (5.3m/s) and grabs a vine hanging v-c:f8waep bak dg:e) 6ertically from a 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 from rest, slides d7o: d4 dm9hjto qm(3lhown 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 frictionlene fb++r(s qb8 to5 rpj0x)tt:, ar2cpss 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 jk(*dha6q ad;) xuib(energy is transformed into gravitational potential energy without the k*i (ahu)(b ;adx6djqaid 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 speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertienz- f7vy(ff)cally upward from the top of a platform with a speedef7ffz-yv) n( 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 constant hrtsf5 r3*z2i is 950N/m is r*i2 5 shft3zrattached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides withou8z b* x2devsz4 / crmxy6suu/0t friction along the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum c dxe2yzruv 4 s6u0/*zbm/sx 8height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffness conwsq.t **kf;gnstant k), Fig. 6–40. The block is given an init t*gfwq.n; *ksial 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 bridge. She is tiednq6+dm3uq w w3 to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness q 3wuq+dmn6w3constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to point 1 where it is8yw55nf)sqe gcbk 46 j lhp4m- released from rest. Assuming no friction, calculate the speed at points bw56 gyfmp n s cj4k8l4hq5e-)
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed oh nl7r (nc- e*s6xspngdj33) of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottom of an vf5-r/ l x7sj(c5 pmxoelevator shaft. If the elevator cable should break when the elevator is acmfxp5 lxjs-/ r7(o5vt a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cyclekkx5)(- h zcsk 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 glv,gbtvw ha 2d9*7c:and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this collision? g29wvtblvgd7a ch,: *$a\times10^b$ J a =    b =   

  A 21.7-kg child descend) ym smvnv :skyc7,c5c6 (*pibs a slide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generated i cm5y(6vvp )sn*c ik :s7bym,cn this process?    J

  A ski starts from rest and slidesz: -vnmw:0qp e 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 m above the ground. rtkkd4qr m7rqhs146bg : 8o do:w,p 6d
(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. 8dk ti:n1(e1bf 8wajp0 m, and it bounces back to a height of 1.5 m. b1kt(ne8f pwdja:1 8i
(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 2) lx9q6 .bnbk1ay6pqto807d jomc il with a constant horizontal force of 350 N. For the first 15 m the flooo66kiy 7j 2b) p1.9 lbqdl nat80mqcoxr is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with mk30c n f;td c9n0trw3a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reachn 0t0kcc3ftr9wn ;3md point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reachtsu+: vti q;rlkg/.cl/y.b5y j;el *ces the foot of 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 a very pt b pjb09d)j0light 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 turnib09bt pjjd)0p ng 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,1kwme he37.:raoi foezrjy sqa31 x((*5feg : 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 positf1ram e.y 3k x5fqgeo*re(weo 1 aj:73(:z ishion, 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 of 980 ka4k9.fkx39u kln5qp jg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speka9kx4jl .kp5uf q39 ned 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 to axuq(0b)we :) dci1m wf sixth-story winqfxb wud cme1 i:)()0wdow 16.0 m above?    s

  If a car generates 18 hp when i ep2pftze5:ew .w q3*traveling at a steady 88km/h what must be the average force exerted on the car due to friction and air resistance?z3e:f p.ewt2pqi w5*e    N

  A 1400-kg sports car accelerates from rest to 95. 6zmtkqije ,:km/h in 7.4 s. What is the average power deliv,itzkq j e6:m.ered by the engine?$\approx$    hp

  (a) Show that one British jsjcvtu);rk9 s, gi4,horsepower$ \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 s3k( wffuik:1baqeh/*i6 a -gare often 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/h in about 6.0 s :o 5wjjb*o9)xhuenan m 08uy5 on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveli n9)*yb uhu 08:o ojew5jnxma5ng at a constant 75km/h.    hp

  How much work can a 3.0-hp movwclx im047y)tor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from resttz7hv3wl/ 6ya;zru*sp1g 1ai to 14m/s If this motion takes 1.5 awy7 6thzs11g*vrpi l;3 u/ zas, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water p ax6bkr4a +qks/ k4ev0er minute through a height of 3.60 m. What output rating (watts) should 4qvb46ks ke k/0a+axr the pump motor have?    W

  During a workout, the fo35m e6l.5u grznbdr wv+ gq+b/otball players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inc3q/z5w.ebv m+ 6ldbnr5u rg+g lined 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 climbm:58yevjz 5 lm9kr7m i 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 maxim:ig+v :q.v x jngpfw6.um power output of 120 hp. How steep a hill can it climb agv gix.6q w v:n.pf:+jt a constant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower mubc9euqb y 2(z mssgf1;8xomof+* w88tst a motor have to be able to drag a 310-kg box along a level floor at a y *z9; (om1w g 8cft8fb+bso8xeuqs2 mspeed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.0mzz dv6 lirsvds(77vh8eoc5*+ h d n,5 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bumpers”pzkj 9 d22pn6yq so.k/ that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permdkzn.s/ kop6q22 j9py anently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf i ig6)-axsc yp9m0k;r fs 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, an)- f 69rp;ki0xy csagmd 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 (Figv qwzdmy;p(/ gbt//s.xnk;- x. 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 y/qdx n pmw ;.xv- /z/tb;kg(s6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without frictiondamx*1t. -rty along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the veryx *damrtt. y1- 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 akqe9lmelycuyp2z, (c,8)s4gircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor in,su k9 qzg4pem8,cey 2lly()c juries. 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 horizont5ph- b9rd r3xc)b73 yht,vxa cal cord of length L whose other end is fixed (Fig. 6d3b9tah,)v 7pxrry bh 3cc5x- –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-h6 w *0i+spe 47w,msxk.(qcwcru*v bhd igh mountain. The climb is made in 5.0 h starting at an elevation of 2300 m.bh,.i*xqe 0+cukm ws(6pd7*swrcw v4 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 abo21- */ g xktgex+.c/ oiektqfkve 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 are e z -m8oy:,ozvgy/xv/a in California claims that its lifts can move 47,000 people per hour. If the average lift carries people ab yoyv ex/8-gzo/ vm:,zout 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at )55 sb8c/lsau, 4nmluxpe :lsthe rate of 650kg/s and falls vertically 81 m before str85,xbl4 )ns aslcusul:m p/5eiking 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 co.dpvcj 9ch w12ct q/r-aster with 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, s . -cpd2 wcht1c9q/jvrix 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 convert a candy bar directly infqz0am9 ky3o 9to work, how high could an 82-kg man climb a ladder if he were fueled by one bar (= 9kyz93aomfq01000kJ)    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 ang6xjy m-k gvcabh;csy10- j-e0 le 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 bathro j: gej6w4sn)rom scale, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the sca)jgnj6 sw: 4rele 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 la+0h: xsf9r/cq-jpn8whps uq*ke (Fig. 6–45). He releases the rope when his velocity-*98 cqj0/h nsw psrq:x+ufph 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 athl nc9 ow5y(4(4se-86iv:kiw )nikq6pamdd ifm ete climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to accomplish this feat9 a45sockpvd 6i wy6(ni-8mqfnedwmk4i (:)i?    W

  Some electric-power companies use water to store energy. Water is pxu nwrvjs y-g0 h69jrpj7q8;+umped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.n gru0jrvxhq96+ 8jw-y js7p;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 kk2n,obg 0e3or5+ pk gin half. What is the spring stif3 bk nk0r+oo2kge p5,gfness constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough im, wi ) hymcpfg./ 6h79fg/wn37 $^{\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/h5v e9x . t*/5zx8yatsskthl7n to 55km/h in 3.2 s, how long will it take to accele9 *tt .nhks x/szt 57yvaexl58rate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patiene 08a9iswwkf( t walks on an inclined treadmilfi sk eaw980w(l (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a distance of 500 mxh+ x7:ra*y sd, what was its velocxdr*sa +y 7h:xity 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 7h2 -griaryq jd0:rq4from 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 ij0-arqrrdih yq:247g ts maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s