In what ways is the word “work” as used in everyday lang2 u ;;urqp l +)h*ad:1dqbitxx5ndg:r uage the same as that defined in physics? In what ways is it different? Give examples of bothxu gq2hil)u1d5tx rqda*d:+rnp; b;:.

Can a centripetal force ever do work on an object? i 2stp;fq3zzm/s:si 5Explain.

Can the normal force on 7m/4aovpr+q cpt;t:o+rude 0an object ever do work? Explain.

A woman swimming upstream is not moving with respect to the b rsfb wv.ce)z3 yu);.shore. Is she doing any worvsb3)wb urc.ey.z)f ; k? If she stops swimming and merely floats, is work done on her?

Is the work done by kinete k1 0s22wslbdic friction forces always negative? [Hint: Consider what happe2ed1ls2 k s0wbns to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you are tuey y*ca,m :*doing no w*y ua,my c*:teork?

You have two springs that are identical c/,4mfym6c sfb, e 64hmoixb+j3, q:dx;hpfv except that spring l is stiffer than sprinm6fex 4 ysdbvqc6m,4j, b+mh xf,h;/ poi:fc3g 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 constaer avem37)z/r7;cv bdb(1 li nnt horizontal 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 by the1 /) rbn cdamb77rv(v;eizel3 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 60(ycego45cpi) yn zodj+ r;lgravitational potential energy change when you jump asj+ ic (dy5zyrelc g64oo;n0p ) high as you can?

In Fig. 6–31, water balloo),)a0a xklvj ( vane6fns are tossed from the roof of a building, all with the same speed but with differ)l6(v 0ax, vfeakjna)ent 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 ac:xnc/hwcac7 pa6.t,2la y /dbove 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 traje7h,xcn2ay cc/p/ cadw6lt a:.ctory, 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. Iz6yha/jx yaj;1g7 y u(f you compress the spring by pressing down with your hyj7u1g /y;h(j xayza6and and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. hakee,er 462o p el*j06–33). The instructor pulls the ball back anda0 , 4erkeh2o*l6 jeep 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 gravitat8ot(x3 srx2z ,pl zl6hional potential energy when water at the top of a waterfall falls to 2 zh ,rp6z(lx38tolsxthe pool below?

Describe the energy transformations when a child hops around ,qj:;nbt ukn9l -/2vk i4uhauon a pogo stick.

Describe the energy transformations that take place when a skie(ca 4pjq al7rf+ s(g+f(h lxn4r starts skiing down a hill, but after a time is rgp(4 +nj s+qa(ffachx(ll4 7brought to rest by striking a snowdrift.

A child on a sled (total mass m) st4id/5y tcz4 gcarts from rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on tc5/4 g t4zdciyhe angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in theiq) w+prs/wdx93h x p:rr path rather than stepping on top and jumping down on t)p :r3p9 qdwx shr/x+whe other side. Explain.

Two identical arrowss.ed.bm xol a,8h 0;ee, one with twice the speed of the other, are fired into a bale of hay. Assumih ..xa 80edbms ol;e,eng 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 s6 fd 8yyjnq*-/.z vpkrimple swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a gr/8z*.yr-d jq v 6fpynkandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than its oe8kbe(xgl*/4n3 uu2 maw* lkx riginal xxe */n ma l kke*2w(b4uu38glheight? Explain.

Suppose you lift a suitcase from the floozfkizvcp;f4mj 9f3jljbme(1)8( e 6j r to a 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 path, (b) the time it takes, (c) the height of the table, a; z1mzjpi jjv496( ) bel38fkmecjff(nd (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than the worq;liwd/8vj/b 2k6 sk3y r+abyk.

Why is it easier to ci6 c;xch/v s(ilimb a mountain via a zigzag trail than to climb straight uphvi xs 6c/c(;i?

Recall from Chapter 4, Example 4–1m rs-pmj+m0xzj5 cj +94, that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how mucj5mjj+ m 0mx -+9szrpch rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 2*jq (hn u;hplqfy +a-965-kg pile driver falls 2.80 m? 9hh+a*(q fl yp; -ujqn   J

  A 65.0-kg firefighter climbs a flight of stairs 20r *i)ye0ze ) h*jwfm/d.0 m high. How much work is required?*h0e/) fz)w *mridy ej    J

  A 1300-N crate rests on the floor. Ho5u0i4-rjw)2 z+is) ax eehlgt w much work is required to move it at constant speed (a) 4.0 m along the fzhiw0ti+ r4 ex-u2)lga5)je s loor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally;j d(csxl2vllhr4*m 5 ) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coeffr;*mj4 (lsl lcx2hv5d icient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force acrkc(grqy-n;t ux)u 1g;oss a floor at a rate of for 7.0 s. ;u t kx)qur1gync(-g;Find the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat p4i:v-drq:gr on a table. How much work is required to stack them one on top of another? -r4vi:pg:d rq    J

A lever such as that shown in Fig. 6-35 canun3xp bw.p t+xb/:u,g be used to liff objects we might not otherwise be. +x/p,gutp:wbuxbn3 able to liff. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° ic7md q)jei(i*ncline and is kept from accelerating by a man who is pushing back on ii qcj*e(dm 7)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 give a/yn* cvwv+ hge2 tar/h4do ),s helicopter of mass M an acceleration of 0.1r/c e4 nvy,ho /gthd)s*+wa 2v0 g upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

  $\text{What is the minimum work needed to push a 950-kg car 810 m up along a 9.0$^{\circ} $ incline? }$$(a)\text{ Ignore friction. }$    J
$(b)\\\text{Assume the effective coefficient of friction retarding the car is }0.25.$    J

  In Fig. 6-6a, assume the distance axis -e* h m*dl5 95)urkvvda2ekz qis 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 object05+ zilfsr o,x, acting along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to movl ,fx+0sro5iz e 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 aqmd0r* +*5h t(lctafa particle acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule, wi+ph zruqgc(d+7c a30oth 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 isg . .6;j2: suuefuzxey doubled, by what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an elec v *b9blx0eoa2kgm/ 1atron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 st3m7 1+hg)+ re wvudmjaop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an averagvv 6 hgllw x+(6-jql7ze force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it lz6+qx7hv 6- gvlwllj( eaves the bow?    m/s

  A baseball (m=140kg) traveling 3 qhk(t23d-bbcjo (g;p k u,u)q2m/s moves a fielder’s glove backward 25 cm when the ball is caughtu b3c2(g,b)pku( oh j tdk-qq;. 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 wikbdt,f m45zgv +-ur7e-tv hd,ll its minimum braking distance be increased, assuming all else is the same? Ignor vek,+g dzrh,u-7bf 5tdm t4v-e the driver’s reaction time.

  At an accident scene on a level road, im.c4 yai(y 3rtw1u*r znvestigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kmyaywc 14utr3rz. *i (inetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By thq,pl 8u6fh (pa9 l9ua9.v6 pgqyzxn9h s6.czae 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 distanceqhcznx , 89 v6fz9hslu(g pl.q9up66 p a.aay9 between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straigxu2dxq 0 dae9 q akc5(w7fghq:91 pxa;ht up by someone who does 80.0 J of work ondf1w kq2 e9 q:d a9u5x 7apgh(xaq;0cx it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m1 0jpa. gu4e1yftl7qf b4(nigc/ rsd , vertically with an acceleration by a single cable. Det(1l.espu4fcgf4,q1j0b yn tidr / a7 germine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/ms;ad8.11sw5h6cy imim hd a 9v How much must this spring be stretched to store 25 J of p;avyc mdm985hiihsas wd1.1 6otential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What wo1+vx0f3zyr,k5s o+/pibz h is the change in pf ,hywzo b+si 0r/5v1+3pz kxootential energy?    J

  By how much does the gravitational potencdx vpmaz 98: 4g+cp2dq9rb*q tial energy of a 64-kg pole vaulter change iqz8q* rdv:9mca+9pc 2 4 pdgbxf his center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontaa0vxy)h h4/jh 5 qckz6l surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest inyh6j q5 /kczav40h xh) 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 ground so it is 2vr95t,d e7ui e.20 m above the ground. What is the pd5uvtr9 ,ie e7otential energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m f-us )x8i .ypi85ppo p*u,yudand climbs to the top of a 3300-m ppyip. uspuy p5xd-f),8*iuo 8eak.
(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 zq*7 rvenw iz;8.4 j83qjhwkgnext to a ruler. The end of the spring is next to the 15-cm mark 3.q8qr7 gn*z8 ev;hjjzk4wiw on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, a 1ij*d9-x yvcis running at top speed (5.3m/s) and grabs a vine hanging vertically from a tall -vida1* yx9jctree 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 down a frictionless 3t7 lnoqow 4:ff hi- /ke,qg*4a5.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a frictionless 28.0, ifs;d(aeue +$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into gravitationar8pinyg 4h69hz. gli( l potential energy without the aid of a pole. With what minihnlhiigz9 rp4(.y86gmum 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 vertically upwaru5jkp a)+ 2k:e:bjpri l(-p tfd from the top of a platform with a speed of 5.0 m/jp kf+:(ipp erb5k-lj)2 at: us. ($\alpha)$ 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 i0lopc*v2 gm /cts mass), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0. cco *2mglv0/p30-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 sl8sympojr, zb ul.38h-ides without 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 height h must it be3s8mjby rlp8hz.-u ,o released?    r

A block of mass m is attached to the end of a spring xg.bux0-1k q 2b6. mwtnhem-w(spring stiffness constant eg0mwxu h-b.m kbn.12xwq6-tk), Fig. 6–40. The block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps6dd2x4 n ke jddb1c88q from a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k ox6b n4j2 qddekcdd 188f 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 dragg6 -x6v.l)w)roav1) hivyoxl qed up to point 1 where it is released from w1yq vo- )vh)ilr)6x oa 6xvl.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 wiwd-e 1yszmdzw 7(yt30zc-:d wth a speed 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 elevatorx22x)pj) qvet a-,gid 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 that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of theg2di2e p xa,vq) x-jt) elevator and passengers.

  A cyclist intends to cycle up ay) z30ngw36ynv mc6h l 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 ,x3u u6 gyrm9btraveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this collision? 6mr3,gu 9xybu$a\times10^b$ J a =    b =   

  A 21.7-kg child descend jeahf4xw8tn+,b*0 njs a slide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much therx*nt ja8,0 +bh4jfnwemal energy due to friction was generated in this process?    J

  A ski starts from rest and 5l9m-myz-ogz-i;7m vcduy( w d,kim1 slides 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 b/h qmz)a(2xxpka qh 8(0 3 :tucro1iuground.
(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 h :p3 955gygmntpp8z xu o,lq(it bounces back to a height of 1.5 m.pgqup,:z p5o5y mn(h 3x8gt9l
(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 5r6c s;.hwvxub58xz oa d.v0x, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionles6ozdvuab5c5r.sw 8v. x;xh0xs, 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 vci: 8,jux6akin Fig. 6–41 passes point 1 with a speed of If the average force of friction is equal to one-fifjxaku 6iv8 ,:cth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady upwar5, jszzug df*:d 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 firml5(xget5 3fuo3gp ls hf474yvdy attached to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It glp 355dyf4eof 7 tu(3xvsgh4is 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 friction between the block and the table?   

  A 280-g wood block is firmly at0rqycs q 4z4n9v-ok,h tached to a very light horizontal spring, Fig. 6–40. The block can slide along a table wherks4 rqzc,0on-q9y4vh e 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 stretch on its first swing?    m

  Early test flights for thdzyij n tsv-zov3(-a dh:*o48e space shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height o(oyi*zva sj4-h3-odt vnzd: 8f 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 pkw3tenz ymw3e.-i mo :dpftb,39z-u6 iano to a sixth-story window -63e m 3z:t-fymo3i pn,kw.tzbudw e9 16.0 m above?    s

  If a car generates 18 hp when traveling at a steady 8jf6e5tft( :cgf-ua +ox9 ,s*ejd :zwq8km/h what must be the average footd +zaje:5 w-g 6fxueft*s:cf 9,(qjrce exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is the p *7ppmsqu, dj5kx:: oaverage power delivered by the eng:xuqj :s mpp*d,pko 57ine?$\approx$    hp

  (a) Show that one British-x-mhwi*k- wsl b9 b;v 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 expressed in the form of “kilowattj op3pppx zz *ylwn8y:)r 7)4n-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 heruuj u8*q5:z czd l(+s9zkbc -x 1150-kg car slows down from to 65km/h in about 6.0 s on the level when it is in neutrac9 ( k:s+c-zxl uj u5u*qdz8zbl. 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-hp motoro he 5/ob/r02zn ec3sh do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest wlm5; bf:wj /bnr0mr0to 14m/s If this motion takes 1.5 s, what average power walmnwjrb5 w /r;m0 0fb:s developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m. What o- lpaf (nucg;/q:2ng a7kq us;utput rating (watts) shoulds7/ up;qgk:f- la g ;u(nqc2na the pump motor have?    W

  During a workout, the football players at State U. ran up the stadium stak5dge. i/p-0k oaf26vrsdlwfct d7q2b1yc *-irs in 66 s. The stairs adqt1-.rc 6kdecb vs20fywo/k -l 7i2 ap f5d*gre 140 m 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 cyclnyr(k6 n 4jo4oist climb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum p pq4ggd9vk3fa 9;;sbr ower output of 120 hp. How steep a hill can it climb at a constant speed ofrd;;p qv9s4f g a9kbg3 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower0t(dz w .r) wskbttt.9 must a motor have to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient rdt. 0t k.) tsztwbw(9of friction is 0.45?    hp

  A bicyclist coasts do*ux, b.sz.lprzn+nn y*zk2; mf a;m/ ewn 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) bumpers” tkiq)gvtz :a.8hat 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 zg:iqv)t8.ak 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 is 10.0 cm ogka ,5.1gmn mvff 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, and an average shelf holds 25 books, how much work is required to fill mmv1g.n , gka5all 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) i8:1o g. 9m4gwqdq ropen the 1936 Olympics shows that his center of mass rose 1.1d qeg8wro4 1:.p9m goq 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 slrm9vd0q)6/abp)4od mt/ 6ngagjk3yziding without friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, ev/4zg ))vdm069 3bn/rkpy qtdjom aga 6en 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 aircraft without his parach5ko zikht9p 8cnd ;).gute opening. He landed .i ckdtop8g5 n;h z)9kin a snowbank, creating a crater 1.1 m deep, but survived with only 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 tbrwvt3qg- 28to a horizontal cord of length L whose other end is fixed (Fi t38- btwv2rgqg. 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 intdx4z 5po)b 1;spuvk7b vp8t, 5.0 h start45b zotkp 8xpsp );vu1d vb,7ting at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks.tklop )cy1zi*x cup1 t/6r y+ when a 920-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can move 47,0kdps4no8s1qg 71dw8(m sb f t600 people peg87sbsw(k1ds 8 qon 1tfdp m64r hour. If the average lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s a+m;6xp tpvr .zdll6v8 ix :hog56l v+dnd falls vertically 81 m before striking the turbine blades. Calculatexvxipp g v6+mh;ld:o rd5t68 l6v+ .lz
(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 hvmncxm9/l25eg ad d- u6.ic*1rgkq ; loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of tgc5u.hvq m* d/l 6a-ge2ix9 nkr1 ;dmche 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 convert a canudbu5 8ujc4d i6myy: 0p4-lm rov7qq *dy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (o5 *:d4vc jb p6qu0 m8r7yyudiu4-lqm =1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward an m8uqa7nl (r, p)wla*mz33agr:6 igr ggle 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, thmr njcjt)g/z8x.iz8, v5no a (e spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the sj.aztn x) /czon8,i5jr mg(v 8cale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s gkubjpnj 38q 1 ye,3ub0rabs a rope, and swings out over a lake (Fig. 6–45). He releak3nu1 be0j3u qjpy8b ,ses 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 a vertical distans4p)+ vfbvwc ,ce of 5.0 m in 9.0 s. What minimum power output was used to sf,vcwv+pb4 ) accomplish this feat?    W

  Some electric-power companies use water to storez8mpgjuis x mg7+)p+ 1yev26 a energy. Water is pumped by reversible turbine pumps from a low to a high reservoir.jmzpp1286ie7yuxsgv +) g+m a 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 thesl -(som s)t hhuwgj,l9;z,8* j urnsdf 1z:2o spring stiffness constant for each of the1z ;ujo9l: ,f nzd,h-lswthsms u8g*o (s2j r) two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough khlzh/a h ;::ncjlo6 2 ql/cwf89xy7h37 $^{\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 acceler;xpmd)q y lj2cho/ 88cate from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power staydhxml c ;/jyp2c8qo8 )s the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patf7j vdbjp9-* *uxift 2ient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a *txb7pvdfuji*j2 9f- 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 vert uwcje;/ u+9xemz:e0gc,n dr5 ically upward a distance of 500 m, what was its velocity wheee+zm; / 5d:n0u9c wxruj cg,en it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height3b k*mgae:z0 t qsw8f+ of 2.0 m at a rate of 95kg/s (a) If this w 3:0*m w+z 8gftkbseqaater wheel is set up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s