In what ways is the word “work” as used in everyday language tbz1wfql w sj-a; *e7 hiu7z4k,he same as that defined in physics? In what ways is it different? Gi* fusz1e 7a wbh jw4lk;z7-q,ive examples of both.

Can a centripetal force ever dr8 ,5b y csi(mbjdi3(-fmy4slo work on an object? Explain.

Can the normal force on an object ev 8zg;on)zyqym b2wu1bfejpu7 n(/t 4 bz,o,0 mer do work? Explain.

A woman swimming upstream is not moving with resvk t 2f .rmrh6dx:f1,spect to the shore. Is she doing any work? If she stops swimming and merely floats, is work done o ,2 t6:v1s. xdfrrkmhfn her?

Is the work done by kinetic friction forces always negative? [Hint: Consider we,slzs1 tnvq 6*k yz8;hat happens to the dishes when yo;,q8 s 6 yn*vkzlzt1esu pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid 4 a(cqe 0vaowcc.q.:awall even though you are doing no workqc0v a(.c c.:eaa qow4?

You have two springs that are identical except that spring l is stiffnrfgu4pvrkaum 1/. ey- - 1:5j tfiw4gx,e5tjer than spring 2r41. w/,1kvte5f t4au5:ef ym j-g-jnipg rux $(k_1>k_2).$ 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 is free :q4sjl57ke 5 zcj j;vbto slide on a frictionless surface k5ql e;z b7:j5 cjs4vj(Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potentiaypo++pgkeoqw// ax31 l energy change when you jump as hi y1ex/p/op3gw aq ok++gh as you can?

In Fig. 6–31, water balloou0h5aw5r2xors( s7 ly ns are tossed from the roof of a building, all with the same speed but with di rw7hsrl oxa552 (usy0fferent 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 its lowest point idz,x:qr ( 7ykbq:e eehmgu: *czd+ 5.jn two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to : ,:. erqzh75jm +bd(egzud :xyekq*c swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress the sprinx jpi//uoa91. 6altxag by pressing down with your hand and then release it, can the sprp .61 t/iaxxaj l9ua/oing leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling byth6k xfal o9 1/o5 wi8bklc4dmj9s4 )y a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ba iaod45k1y 9/4wbcth js )lxok98m6lfll against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when water at the top of a wa,8rx(tqjzw ,zogn;dd grp5.,terfall falls to the pwopdt,gd;,znz x,j5 qr. rg( 8ool below?

Describe the energy transformations when a child hodp2w*cta eiu0 s 4)ut,ps around on a pogo stick.

Describe the energy o,z dy 2qf/n9ptransformations that take place when a skier starts skiing down a hilfy 29onq/dp,zl, but after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts frk 97o,rbxrhi h: nf66hom rest at the top 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 fricthbif 66rh7no :xh rk,9ion, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rather th / o-1:i ta e8ulqai7yn( vq8r7xcis;nan stepping on top and jump 1na;vxe8sclq a7ut8o:(7 nqyri i-i /ing down on the other side. Explain.

Two identical arrows, one with twice the speed of the otr1s- yhe; wo99opamm 4her, are fired into a bale of1 hpyr 4m s;w-aoom99e hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy, (a) ig e+s8 nw/s2 l1fzx5ojty0sh *bnoring friction, and (b) taking friction into account. Exwsbo/slhxzs5e+ j n1*0t 82yf plain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound tofir+69gp f: yo a height greater than its original height? E9ffi +o6rygp: xplain.

Suppose you lift a suitcase from the floor to a table. The work yb*drpl( d2 y /sqw8.syou do on the suitcase depends on which of the following: (a) whether you ydr*q2sydwb s8 / (l.plift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than ()xk de)flkk-k0 x*ijthe work.

Why is it easier to climb a mountain via a zigzag trail than to climvlt ;e at0p*cw6;.eu u(zeat(b straight upt leu6evet ((zau w t.0p*;ca;?

Recall from Chapter 4, Example 4–14, that you can use a 6 o.w1j+ io1w1uarditpulley and ropes to decrease the force needed to raiseto 6owurwjid1.i+ 1a1 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 wr fgb tbm-2-d6*y9cq rhen a 265-kg pile driver falls 2.80 r*yqg-m b 2rtb9-c6f dm?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m:wrvi* )uuj v/lg ;pigvn;7/p high. How much work is required? ui/7gl n;i pvvvj/;wupr):g *   J

  A 1300-N crate rests on the floor. How muchezkl.2ci 7 t9x work is required to move it at constant speed (a) 4.0 m k.97 ieclt xz2along 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-/no m6h0g9dcowy1+ dddh4oguj jq+. 160-kg crate 10.3 m across a y.h0 1u/ ojjog-odd gm4dqndc9 +h6 +wrough floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accyjhi ugbmye72 .d :/4dw 5 thrn)-e,tielerated by a force across a floor at a rate of for 7.0 s. Find the net workdi7dw5in rh2tt e4-ejybg :.)yu h/ ,m done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg7rqjr0y 5ke wvkzht2 is /v6/j /y2lw,, lie flat on a table. How much work is required to stack/5hkr20t lyvz 2//rq 6w 7jsiejk, vwy them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects we mighj3bscf7mp i+8 t not otherwise be able to liff. Show that the ratio of outpbf 8+i3s7mc jput 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 downb9j 8gha3g5 ln a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficienh 8gj93lbng5 at 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 helicopter of mass M an(i )s+ mduv-fr7 rz5av acceleration of 0.10 g up+ ds- )vmaiuf(r5 zrv7ward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume the distance axis is linear .rjn,r uion6s59l mzs0)uky g(ou) s1 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, w3)cag,cgzdp* g he 1gzio(qw1: zp;. acting along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the q:g,zpd;e)zo* gc1gacgw1 .pizh w (3object (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 acts itzug)8:1etg 5x*w ophn 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, a a a4g)0b0kjrjn 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 its speed increased? j rr q2ms--z1ed,4n nd$ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is reqt2gwi6b7 l qm- en(0oeuired to stop an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kno u*hro(6sc 4gcar 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 avrttn qz1 o8,z gwgjrs u70h7x)0(wr9rerage force of 110 N on the arrow ovr ox8 )rnth0r(sqj1 wz,ur9g z7tw0g7er a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fq81 wjt 0emo*sielder’s glove backward 25 cm when the ball is caught. What was the average force exerm*w1q tjs o08eted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its minimum br3 2ph odx+fk5 o4(xozqaking distanc z+o5 q43ox2dfxpk(ohe be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a dhzf )q 8gjv3n-+a)ylyz nh, 5level road, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and ld f8 alzn+)v,qjh) gh3n-5yzyocked) 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 the time it reaches the pe0z5ye . 5hmxeluh 6t3late, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance durinm h3 e55uh0ez.x 6yetlg 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 straightkqv0,j4b1mx4 2gluqj + h)tn,jmkns3 up by someone who does 80.0 J othvbj mx+jng3 q)kk2 4 q1j4sl,m,n0uf work on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by yo/q 1l7h*dmg a single cable. Determi d 1*/gyhm7qolne
(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, kh bxrx5)w9j d/1)bjys(1wiiq, of 440N/m How much must this spring be stretcy/bhijj1b x9(xdq1w) w)sri5 hed to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to an6zsfu1vc :ne*(n0ke)xqa x c9 other 1.2 m higher. What is the changecn0a (xzv*ucf ne16x :ek)9 sq in potential energy?    J

  By how much does the gravitational vhmv8 eay:o-oev y :gr,v 2r23hdo.s4potential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m d2s8hy-y vm,vv r34ve2h:oooda eg:.r uring the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h whgtl06 l-n jmm0en it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant 00glnjmml6 t- of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it a0 *h/qj9 x 0manf.c e.nac.sqis 2.20 m above the ground. What is the potential energy offh/a.s*c n.xje0c n09q .a maq 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 anda, zavr hl p1v0)c37dq;p)z7 xv ek-oz climbs to the top of a 3300-m p zqd -p0h) 1vr, 7;azckz3)xlvpov7eaeak.
(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 ruli n5pw0hef 2z9er. The end 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 0pzwh92fi5n e ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3po )mw d;8aw pv ho0 hdm2ra3s;4k+5okm/s) and grabs a vine hanging v2orpm map) swdho8 0;54va odkk+3;hw ertically 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 down a fricfuve01r ,pl:n tionless 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 frictionlezk1an,h j,gk+3 qkp4qtn d3 zn.m-o2css 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 itr4z/u.8c afae: p omtb 3-wj)(2owiys transformed into gravitational potential energy without twafz y-t eci o.2poj/w8brm4)uta3 (:he aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from 8oqthce qn*hyx:/a +hc n087f the top of a platform wita*7tonc:+8 neq/0cyhhh x8 qfh a speed 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), whosep/2m 6 xt(ieln spring stiffness constant is 950N/m is attached to a n(e6tmpl 2 x/itable 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 without friction alo2skyx :d m4v e.qv((dfng the looped track shown in Fig. 6–39. If the block is to remain on t.v s4 qk(xd (e:mfvyd2he 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 attached to the end)c- j xykpbk.dp,,cj+wf h2k ; of a spring (spring stiffness constant k), Fig. 6–40. The blo-c+jwxf pd, .p, cbkyk;hk2) jck 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 jumps from a bridge. She is tied to ot)d6npqvt b.*cys. :a bungee cord whose unstretched length is 12bd)qscoy:. 6pntt.v* m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to point 1 where i at3n,+c hf2pzt is released from rest. Assuming no friction, calculate +a3fc t,zh2np the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a sd9i(7yy *+ dox pp8t+)pklx cspeed 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 sprxxy q:nmmr(c.y+ eoc*i010 xw ing to be placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undxc:xy+c y.( e *q1 mom0ixn0rwergo 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 cyclp(f+wv6pxv6.mtn byv 6sr1 x.e up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traved8nqgok)ft 7v m3z+l 6ling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this collisionkm)v gnd7f z6l+qto38? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slidxp; :0qwgk. ade 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generated0. gx:p akq;dw in this process?    J

  A ski starts from rest and slides dq)uf3z4nj(2 /y -ibre j-hj kdown 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 droppesbkns8zlx2 6 1d from a tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to a height of 1npwd t;jlin 9nr7l4 v(2a:j z23lh7it.5 m7 irn(jd :wllj;a 7i9vnt 43 lzp2tn2h.
(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 wittm m.c:ijyk4 8h a constant horizontal force of 350 N. For the first 15 m the floor is fricyt:i.c jk8m4m tionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point wx3ptmct *j2x k e;,.v1 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 ijc;.,2kx t w*m 3xtpves 45.0 m. $\approx$    m/s

  A skier traveling 12m/x fm17ioo,,ixbnz:lob it8bc rk1 8 2/s reaches 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 fe7rae9j okx ;n2a1sik/ft8(very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed akf/;79 8nkf j21 at(rosee xi5.0 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 attacyvoyk4i zmfibr: ( 7 go90)0grhed to a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. Ig0ioy ky 7o v()9 bzmri4g:r0ff 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 the space shuttle used a “glidzh js4rf(rq3 r.;j ry,er” (mass of 980 kg including pilot) that was launched 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 abr y,sz4r (.q3rjrfj;hsence 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 l5ftl+(9y 2/6dhkak od vm) sjcift a 315-kg piano to a sixth-story window 16.0o)/ 6yc 9 v(js+kmh5 t2dlkafd m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what musobur a6b.j :yf) 2e0nat be the average for jbfnu: 2.oae b0)y6arce exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/hvn13 h 0;f2ysj+jzbwtbux d+ 1 in 7.4 s. What is the average power delivered by tj0 ywdt3+hsfx2+un 1bz1jvb; he engine?$\approx$    hp

  (a) Show that one Br fea fy;3 i+-p+lwjf*/ts2y ltslb-:yitish 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 “kilowwtgt83 ;uj)(zo 4k-d ic/grsfatt-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/hcup l*/cm3fm-7c dg a5 in about 6.0 s on the level when it is in neutral. Approximately what power (watp- gf3m*cd7 ca5l/mu cts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in ,msrmkiy:8o;bk6 zq 6 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If thwu tn0+2vb f1nkdz+ rx7gqx** is motion takes 1.5 s, what ave+q*r unfkx07* dw+g2bx1 vtz nrage power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per mise*iy68n d sa4nute through a height of 3.60 m. What ouiy6s4 * nads8etput rating (watts) should the pump motor have?    W

  During a workout, the football players at State U. ran up2ix86)z ++t - a wocmfjyxyqs: the stadium stairs in 66 s. The stairs are 140 m long and inclined at an angle of za6 m)tqxs:x-+jy2yco+iw 8 f 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 9zvrn nb7y ytau 609r5climb 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 power ouk p fe);4g.bcdtput of 120 hp. How steep a hill can it climb at a constant spe;).gcpde4bf k ed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg y q:quepvk/z3 et+5l: box along a level floor at a speed of 1.2m/s if the coefficient of friction is 0.45?tzv5p/q +lu :3: kqeey    hp

  A bicyclist coasts downx09xol8-jnn:nhx xbkq+v 3- s 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) bumperst-zzpzin -byf /uii;jr*. b 6t0s).9 msbk j9c” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what musbz c0;btknyu -9 r/j i*m6tbiijs f9s)-..zzpt 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 shw 1dt 9oq ceoz3li/1l.elf 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, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the fzce9l tl q3oid/w1.o1loor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Oly ynzzihj,/g58 mpics 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 ifny8i5,j z/hzg he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding withodkx4 gps*/hdp +bhq1s qn*g .v1;s o.kut friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the loop of ra+nb/p ps. 4;kd *x 1odq.1hvs qhkg*gsdius 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 i2nfxu gwyx6c 01/ji hmwkxw5f(2 :56 jexu5zhis parachute opening. He landed in 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 2x/6inx f (x :uemw5w6gwxz ciy2ujkh0 j551fwas 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 horizontanm;z+tw (-fg bl cord of length L whose other end is fixed (Fig.bt- f(+nm;wzg 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 l-m;-wdrvq rfh352p6ut 9mpp made in 5.0 h starting at an elevation of 2300 m. Ca fm2 ;twmpr pr6h-5pl3uv9-dqlculate
(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 tn;9j5 d v, q)mdqp*po28 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 cekjozpui8 l jb9 m).j *s:11esan move 47,000 people per hour. If the average lift carries people abo1*kj8j)19b .lssm iojp: z ueeut 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls verticall/ +cp0s qc6/y uynke3hwbea1 /y 81 m before striking the turbin 0n6p/h3wbyke /auc1qe/ sc+ ye 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–t*.8y kvd vqwsosp*2544), the difference in your dky*p2 5s *wv.8otvqsapparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could conver.2bko xliy1/ ct a candy bar directly into work, how high could an 82-kg man climb a laddexliok2y.1c/ b r 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 upward 8ggg78mxs :0 l kxn0vbangle 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 springk:suh w;avu2of1j5 : o inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height 2hsfkvwo: 1ou u;:a5jof 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swing d fsk,6f1nlz;/ao4l 2slp;xj (x hsx7s out over a lake (Fig. 6–45). He refnsx;ojdl 7 xfxkp1a( z6lh4 s s;l/2,leases 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 athleteov7)8 dob m; sdd4nqh hs7f:1b climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to accomplish thif7:b dh4ds nv)b;s8 7 doohm1qs feat?    W

  Some electric-power companies use water to store energy. Watebluai ,8q4 pt:g:c) s4v hgwze-nq 9;nr is pumped by reversible turbine pumps from a l)znls hbw9: g 4eu;ig- cqt:pq,v84naow 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 thap /nru*y;hnsdw e7-.e spring stir/. and* -7yeunh ;spwffness constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a/hoqfc3 y. winavd+ 7akll(/2 rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate frqy8 b aqv5q5 f3n -:qb(xg1qe9lph 2bwom 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 stays the same, and neglect friex l b953w 5na:f( 1qgvyqbqh8pqb- 2qctional losses.    s

  In a common test for cardiac function (n; d)mow :arz5the “stress test”), the patient walks on an inclined trerna )5m:;wodz admill (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 l zcgy 6+0a+zuvertically upward a distance of 500 m, what was its velocity when it left6++uc 0gaylzz 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 +momxe +zf .:wheight of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricityfz we+mx.o:+m output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s