In what ways is the word “work” as used in evevt2 t (4: mvckl7:qjic:yoio1ryday language the same as that defined in physics? In what ways is it different? Give examples of:1(lv cc:tto i 72ykioq vm:j4 both.

Can a centripetal force 9p4u uq-eky,qever do work on an object? Explain.

Can the normal force on an obj+ c37ur nt-wo(,5r5tfe0aw8 4eaunn5owpoylect ever do work? Explain.

A woman swimming upstream is not moving widz /yeee29yoi2tmh4 /q sx-0zth respect to the shore. Is she doing any work? If she stops swimming and merely/z4yh-e desxe0 2ymt 2oi /9qz floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Consig7 ndu+j jy)0cder what happens to the dishe+c)jyg0jnu d7s when you pull a tablecloth out from under them.]

Why is it tiring to push hard5ia /2 w1todjt-ddp/ h against a solid wall even though you are doing no w-t2idta/ dwd 15ho/pj ork?

You have two springs that are identical except that spring l zdp(. m0oh7ad b1gzurh 1rsa6q 300iiis stiffer than sprimqga3hria h01z.61 orpd u 0sid( z70bng 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 ho v g1-e) tc2vg3cztbn0rizontal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by2v-gb13 evngtc0)t c z 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 y0fqzk92wy gx;(y . je1tqj.kb12 actoour gravitational potential energy change when you jump as high asgqx k2; o ttq0zw 1bj 9k2.1acj.eyf(y you can?

In Fig. 6–31, water balloons are tossed from the roof of a bui) m(c gu6se8aklding, all with the same speed but with different launch angles. Which one has the hs )(8g uec6kmaighest speed on impact? Ignore air resistance.

A pendulum is launched fc8+i/f(s(agb/*ha5w uiyw ztrom a point that is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajea8wsut/((z i/bihg w+ y5ac*fctory. 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 compf: +q)fx+b-.e 3 2tfpejehwaw ress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, usingx-f:+tfq aw)je .3p hb2fe ew+ the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). T*+ma xpcj +-qyhe instructor p*+ypxjc+ mqa- ulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential j/fmka. hg-. r.jsid mj -p2j/wuf9d7energy when water at the top of a waterfall falls mfd-r./fj 2u k./. m7j-gwsj9 hajidp to the pool below?

Describe the energy transformations when a child hops around on a pogo sticgbgti )x5g6 fr-upb 01k.r5cp k.

Describe the energy transformatiog/) tg,cvf3lyuqq4 ap;1s rh0ns that take place when a skier starts skiing down a hilcfsa gl0;)h r qp/4tg3yvu,q1l, but after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts e7n2b(wgxrrc6 tg /5efrom rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend xrc eg/n gr6w t(27be5on 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 too0/nqy;f:qyhdun3 l 9 step over a fallen log in their path rather than stepping on top and jumping down on the other side. Explain3hnq0uoy :ldy 9n/; qf.

Two identical arrows, one with twice the speed of the othe/s22kc .0sx2. zt jds.b bpooqr, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, t tsobbpj c/x .0k222zq.sd s.ohe faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terl6t*xwu7u 2 zzms of energy, (a) ignoring friction, and (b) taking friction inzl x*u7t2wz6 uto account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height gy:k;:eqa ftu rkwj 5d xx.t;)dj)qv+/reater than its origin)wk) dtj tjxq vueyqd; r+f:k ;ax5:./al height? Explain.

Suppose you lift a suitcase from the floor to a ;gns0uhl e;* scni:*h table. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated pat: su0ln ie n*;ch;s*ghh, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than qmh ru 6q(dmx*vf 17k:the work.

Why is it easier to climb a mountain via a zigzag trail than17bfvz/ w4xp(j pqmh8kou 25l to climb straight up?/pl 4h1o 8k z5qvj( uwbpf72mx

Recall from Chapter 4, Example 4–14,s1a: apo/o+uu; tak- p that you can use a pulley and ropes to decrease thk ;t-a/:pp auao u+1ose force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pisv6 5 ec7ykp0yle driver falls 2ys 5y7vkce0 p6.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m highr g x6/.1 +rcxieo093p f7rvcc6i sa:uvvxhn; . How much work is requ6ips 1376oc0hu e:xrvc.; /acvxi vr+xfr9gnired?    J

  A 1300-N crate rests on the floor. How much work wamdz 8f9nmn 475glr 6is required to move it at constant speed (a) 4.0 mma nz 8d6lgf5wr9n7m 4 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*kfl9 q7pl) dk) pushing a 160-kg crate 10.3 m across a rough floor without acceleratiodk7*lfkp l)q9 n, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg 9 cdto;q* (bfyw( gea-is accelerated by a force across a floor at a rate of for 7.0 s. Find the net work done on the boxobtg9e;w*c-((yaf d q.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. How m3rgyd w-a:4jpge6r 2m uch work is required to stack them p:r2 6r-4 3ggmyjwdae one on top of another?    J

A lever such as that shown in Fig.z)-)ose-m u nf6a qps9 6-35 can be used to liff objects we might not otherwise be able to lipu9-s eqz) )s-6mafnoff. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° inc2c yr,xdc2mz*q 87rzg line and is kept from accelerating by a man who is r2xmqcdz rg*z 827,ycpushing back on it parallel to the incline (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 giv7q: v+wq/v9e7k evkede a helicopter of mass M an acceleration of 0.10 g uq ekkev9/d ev:+7v7wq pward.    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 fhb .7+cex- k4e8ntxzis 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, a4+z9tdn-msll i3 gabz uz 60p(cting along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to moal zm9t -6dz szp03l nugi+4b(ve 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 particle :xdpkai,* tf,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,n/*0bbt xpm* v an oxygen molecule, 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 what factor has ir(k:mbq7weer59 9gi40 tav dwts 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 electryf4nhg:4xfi8e/o4 qkon $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 mnd, qu y.pht 36 nvqvv(gj700traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts ancmg lpiqgtw:2(1 i0k * average force of 110 N on the arrow over a distance of 7ig21: m* gpkit0(cwql8 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25*w):p r mx:xsbx:pdp( cm when:xx* xs(r :)wp mp:bpd the ball is caught. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor wivl-1b 47*84ajlcizxhstd s-jll its minimum braking distance be increased, assuming all e7s-ct l- 8ijhv4 sa*4jxbzl1dlse is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigaty i:y g,kosi78;w ;vezors 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. (g8y7ei ,; y: svik;owzWhy does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched ap -h;uwo0nv43i99 itza t5n vqt By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force ow4q9-;0h a vt o5n tipi39vzunf 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 go if thrown stracl z ,sznpk188ight up by someone who does 80.0 J of work on it? Neglect ai1kp cz 8s8nzl,r resistance.    m

  A 285-kg load is lifta ee e2,3q7cyted 22.0 m vertically with an acceleration by a single cably e3tq ee7,ac2e. 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;kn:.nt4 f83tppaxt;dzcqqk:j 0 + vi , k, of 440N/m How much must this spring be stretch .kj :i3;dtc+ ntpn:pt z;kfvxq4q08aed to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to anotherft:h ofl3f+:j 1.2 m higher. What is the change in p: :3 lftjfhfo+otential energy?    J

  By how much does the gravitational potential energy of a 64-kg pole vaulte9 ;a9gt 0fksacvo4vf 34 m)tcvr change if his center of mass rises aboomt4v f90aks 9vcv t34cg)f;aut 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h b h:jx27 )ee/hrx-t wrwhen it strikhrrx e:2bt h/j-7 e)xwes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book fsh)* h+ey1hl i6cr st kfcaa9n8l4 18xrom the ground so it is 2.20 m above the ground. What is the potential energy of hl)l trs1axeh fc a*i+c4n 68sk8y91 hthe 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 toph: kx09 k*ju-fjph ;uc of a 3300-m peu9p*kjx hcj0;: h -ukfak.
(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 efpyrwo5,h8 6v8dy) pe nd of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the)y8ry6ph,o5 wp 8vef d ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/ 7,;bpc y0cjl4hosa b;s) and grabs a vine hanging vertically from a tall t hc y;4,ljbc;p saob70ree 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, startinu0bs c(ie-e9 b g5wun-g 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 a0tqv,mxqx32 3i r dh9a shove up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed ig2,f nfyt 3gb3v 7oo:qnto gravitational potential energy without the aid of a pole. With what min2f: fgn7o3q 3vt,yobgimum 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 am3+0 mv/rxtafrtist jumps vertically upward from the top of a platform with a speed of 5.0 m/s. (3/m 0+fvarm tx$\alpha)$ 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 constabc(;lwcz5i 5 *x-yqh lnt is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward5 zb;c wlx(lq yc*i5-h 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 witho8p5 a7fcaqjw9c w fa2ruk0:1qut friction along the looped track shown in Fig. 6–5w0aakaj:u rcf7f 1w2qp 98qc 39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attach f,1vl*jlvd5e)-lqa r ed to the end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial vad,*l)-llevqrj f 15displacement $x_0$ 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 briw*go*(6p th rwdge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hor*(gwhwp 6t *ooke’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 khg;-)dsua z )up to point 1 where it is rele d)g-) ;kzhsauased from rest. Assuming 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 spe a5)yzipf dw;sgj,6q;ed 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 ajgmrmw os)8 :0t 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 sprin m8w)josm0: grg 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 cycl uuq3(8d 9mp*c+p pqzje 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 76501( 8dt(mhf/-ptmqw nw kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this c p-mtt(df 1nwh8/m w(qollision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a sbk i1oy.xll6;6h.evl ws 6s+hlide 3.5 m high and reaches the bottom with a speed of 2.2.l;6be kiyxvw 6 hs.o16h+lslm/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and sl; .hho li0vs-rsk*yp)6l ai7 p 2-ybxkides 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.* yzgx6e/aa ,h7dufpc+f 6.xj
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to a height/o eyzj4 s)*o.qnf9ej of 1.5 m)*q4fo oyj/.jeen9 zs.
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulled across a floor with a constk vy641wsz8 zgant horizontal force of 350 N. For the first 15 m the floor is frictionless, a6 zy4wsg1kz8vnd 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 hs, os ns,o21hpoint 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.2sh ,,hno1oss0 m. $\approx$    m/s

  A skier traveling 12m/s rq4 mt.: )-xhvxj n3gfqeaches 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 light horizontal spring (rvgbpddbfeud5 fjt+ (8kg g8 -*5tk)2 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 the coefficient of kinetic 5p+fktgg8b) djk2d *85ev(t gdrfb-ufriction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontag8ewl) 2bte6*x wm upkyah*,b22f7p wvd m -s/l 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 equilibrium position will it stret2vg)we7 wlp2- mx2pf8e*6/ uahsyd w,ktm* bbch on its first swing?    m

  Early test flights for the space shuttle used a “glider” d9 98cg5cynn t(mass of 980 kg including pilot) that was lacc9 gnn98d5t yunched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have 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 m fosnfm ,37vj2otor to lift a 315-kg piano to a sixth-story window 1f7smf o3 nv,2j6.0 m above?    s

  If a car generates 18 hp when travelinglp+:vok+p6xd b70w wlsi l;w-//yrff at a steady 88km/h what must be the average force exws 0rlbyiv6dlxfp++7/ /lw:;ow f k-p erted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95kd6tigqj-b.z 35 fw.-4 ke*ph :z edfzpm/h in 7.4 s. What is the average power i- z.pdk*j4q- dzpe 3hw. g:z6 feb5ftdelivered by the engine?$\approx$    hp

  (a) Show that one British42r bkwh929yr*6w wyfr g mzhzj .:df7 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 are often ex7)x ssdtkf8nu,o: yh5dik39 ypressed 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 abou+q15h5o6ro hxjs vq ho9- jc9zt 6.0 s onz5o oq+jjh9r5oh xqs6v-1 h9 c the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hpxsdd 8nz-12;1hyyte(ru ux:a motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg sy s7re5 vq(zr :( .:m0vihciiohot from rest to 14m/s If this motion takes 1.5 s, what average power was developvhrm (ose5cii(r7 qzv:0.yi:ed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m. What sjv ,5 (eoeeg8xuxo w94h9sc1 output rating (w, e5e(vx94gos1ex9 s w8hucjoatts) should the pump motor have?    W

  During a workout, the football players at Stataspljv (p)*c1 e U. ran up the stadium stairs in 66 s. The stairs are 140 m )ap jspcv*1l( long and inclined 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 6byyhp6zfq +/)s(,ckhtz7 j)i.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. How steep a hill7 f ag-zoy y2uvs)9*w9gvle2h can it climb at a constant speed of 75km/h if the frictional forcesvae 97h w*-v)g lyyfzug2o29s add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able 3u7x( hxwg/t6d hurt)wj l+g5to drag a 310-kg box along a level floor at a speed of 1.2m/s 6/jthh w5t+gug3x7 l )rdux( wif the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7. iat1wonpcy*0 0/db. c0 $^{\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” tha2l r(8nqk -m( c:pvphct 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 2(q8hpn( rv-lcm cp:kpoint, 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 fi 4xt(p a is35fz9/dvngrst shelf is 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, an5n(/gxt d4vs if a3pz9d an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Olympics shows p 9 kyrtiogy4px i())mp6v5z; that his center of mass rose 1k6)i 5 i(o;ztpmyyxvp ) 9rp4g.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sl1x4b hj1x35g: c tjsakiding without friction along the looped track shown in Fig. 6–39 is to remain on the track atxj3115cakj:x 4thgb s all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an a 7qteb 0v*ja3 b dw6guur54f:aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Ass u60qa*d w:5vu3abjg4 7tberfuming 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 jdx2ptwdlw 4 x/6 ag.)eadr)hy 94c u7is fixed (Fig. 62.4d6 w hrj t9x lpe ca7yg/x4)ddu)aw–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 climqc5bav9f, 2ry6fn t ;eb is made in 5.0 h starting at an elevation of 23ce v; ryb52af,9ft 6qn00 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 abovexu-57a)2vo++ n3 htogo4i: xaikxa dp 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)cw-f*1vb qpem q5m:yt a s5n7 move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, es*5ym5b-mc1 t7wq:f)nqap s v etimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650)3. pc4p.xfurbz 5qur kg/s and falls vertically 81 m before striking the turbineuxq3 r4fpcrbuz ) .p5. blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (Fig. 6–4on6 n*u). a(/mbzn ttj4), 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,a.j ) /mzt*nu6 btonn( 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 convert a candy bar directly into work, how high cdx*5:tyteq wt.ztp6-dy d t.eu0j8 0xould an 82-kg man climb a - zx pt tt0w0x:ud65 d q8te.tjeyy*d.ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upwart l-0 k f5+tb42acybnkd 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 scal itpzrod65(s g h7u-,qe compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a het ,( ozqr-s5uhi7g6 pdight 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;5q(fhi 7kwtilo5n 5/ttl uf+ out over a lake (Fig. 6–45). He releases t(ulthwf7tq/t;k oii+l5n f55 he 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 a vertical distanw 167dap gv7ulce of 5.0 m in 9.0 s. What minimum power output was used to accomplish 6 wuld77v1pgathis feat?    W

  Some electric-power companies use water to stor49e0ua)goh*r b 0sj s3pok. qkuw,. .tf)jazc e energy. Water is pumped by reversible turbine pumps from ae j)3,pu0kj*ssf ag . w t09k.4hoqb)ozuar.c 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 cut in half. What is the s5t4oq f4ji7kcpring stiffness constant for each of t4ckfqi4o7 5 jthe two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rougbq )yp1u5h 1n/7gpxkqs )g4sx h 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 frhrqlp/60y kmc9z h8y.3m :kobom 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume ther8qy0hm 6lozy3.hm p/ :c9b kk power stays the same, and neglect frictional losses.    s

  In a common test for cvv4v ,z)yx g5n) brgo5ardiac function (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle y5r4ozbvgg5) nx v) v,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 uxjtb, y*iw3i -wm2pr)pward a distance of 500 m, what was its velocity ib m,*tw3 wy)-x rpi2jwhen 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 ah j.hyh)smat1rk*4-u2z sl0from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is z)t yshl20 h*jmrhs-k.4 aau1set 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