In what ways is the word “work” as u7wpaqqy2tnft5zr 92zy:je5n ;s30m2cl8 c xesed in everyday language the same as that defined in physics? In what ways is it different? Give 2 np:m52l y83 q7;0czynect f 2e5rzsx qt9jwaexamples of both.

Can a centripetal force ever do work on an object? E*,(iyn9 rzn-l 8 psmy2i7z hesl8n)xlxplain.

Can the normal force on an object ever do work? ol-z4n;2zz s gar8b.otbe hu4))o+qd Explain.

A woman swimming upstream is not moving with res9a:3ku/k ncgy q,mde d/o+:aupect to the shore. Is she doing any work? If she stops swimming and merely floats, is work done on h:q,ag ek9 3o: m unca/yu/+kdder?

Is the work done by kineti,j l ynmx405vkc friction forces always negative? [Hint: Consider whaty,k05 l4 nmvjx happens 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 doi*ra yv yqcy 2(r(l e96:w6 6lq2iqpkding no work6r(dyqcq :v* 2q9l y2yai6lew ik(6pr ?

You have two springs that at3 jy-)f gy g2d-bgf3are identical except that spring l is stiffer than spriyja3 fyd-) g 2b3tf-ggng 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 horizontal force on a block that is free to s: ,;6jh hyyny j+(usywlide on a frictionless surfacew+yj6( n,yhu ;ys:y hj (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 potential energ.g sdl uaztju 9pw28o6fr .7*cy change when you jump as highwglpsfz c 8.7 ur69*tao.2duj as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, ap .f wamw*7e.z(o0ee all with the same speed but with different launch angles. Which one has twpe7aef .m e.(za*o0 whe highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a heka(eh . z:y7xr y+pub(,sue;gight 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 us uy(a,g:rby7.k(ez px;euh+ pward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compw*efsh 887 sb 0h( hn,g2ijndnress the spring by pressing down wi288sf ewnni,nh*hshjg0d( 7bth your hand and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire jxo+id5da. yeo hk.dl 8g0;e.(Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supp oke.exh oi .a08 dgd.y;dl+j5osed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when water at ti(lxtuz(;tvywc t7 6 )he top of a waterfall falls to the pool belozx7 vt;cltt6i w()(uyw?

Describe the energy transformations when a child hops around onhpo.c: 30hit d a pogo stick.

Describe the energy transformationsq1-vvn1q91stmz1tb)p 8 ra ol that take place when a skier starts skiing down apmoqqrztv1l )n1 8 9vbst 1-1a hill, but after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the topiy6r+oc dy6/kui p)wsqi y)35 9n zq8h of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (6qy8 6 3hwin5p)qi /r+z uycki9yo sd)b) there is friction (deep snow)?

Seasoned hikers prefer to step ov4fcgo omci :90er a fallen log in their path rather than stepping on top and jumping doiococ90gm4 : fwn on the other side. Explain.

Two identical arrows, one with wdvc4ue 5graaoju)a/s(i6 7b )l9 *gutwice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a conseu) u)usc a54g69j (ag/drowl abiv*7tant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion o *q*iv)8evpvu f a simple swinging pendulum in terms of energy, (a) ignoring friqeiv up8 *v)v*ction, and (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater th ldjpvxm9rqt5t6u94,xv7r6a an its original height9r7ua5x 6jplm tvqd46tx r v9,? Explain.

Suppose you lift a sujx9oqi:man/2h+)tlwt; p 0a vxr * aj/itcase from the floor 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, and (d) the weight of the suitcase:la2*mt 9jn)r0itp oqva+wx a/x;jh /?

Repeat Question 22 for the power needed rather q9x 50 ))t:,)nlhx pav wbfbiothan the work.

Why is it easier to climb a mountain via a zigzag trail than wmrh i eqqwno3z 1qo5yd 753)f9t/if/to climb straight up?f3/wqi5yoeq7 do 1 iw3r fqt)h5zn 9/m

Recall from Chapter 4, Example 4–14, that you can use a pulley and8/ya*e,wmjxv5 pu oa:x0 dfh; ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope mus8yvfxupm:e0*xa ,w5 joad / ;ht be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force whub i+)6kyai .b*bq2vwen a 265-kg pile driver fallsy*u w2q+)6baik bi.b v 2.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high+77g7 l sjv;f 7nhmiu/wz+b sd. How much work is requiregdm n7;w7b/+ +ji7usfzlv hs7d?    J

  A 1300-N crate rests on the floorb m(mjm1w. 1bb3zoqh,99 bnor. How much work is required to move it at constant speed hq.3r9(bbmbo ,o mzmb1n1wj 9(a) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg cratp x.sch,jvd* 9e 10.3 m accpx.,djs v9* hross a rough floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor atilg jn5rtr9x2 .o2k(v a rate of for 7.0 s. Find the 2xv.oj ntg9r2 (k5ri lnet work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lis.wp3erz y-v(p kudy: -9n. cie flat on a table. How much work is requiredryu-z . s ycdepn:.w3pkvi9-( to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff +l-;k sak2 avp*bc ygrn3a7)lobjects we might not otherwise be able to lifrla7l+av k;- gy3p nkbc2a)*sf. 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° incline and is ken fgwofc +2mdn/uwa9 y9m; g1/pt from accelerating by a man 1;+a9d /f2m/wgmoyw 9unf gc nwho is pushing 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 give a helicopter of mass M an acceleration of 0.bejb*7qbw(e7 m wi 37k10 g b7i 3q wbj7ewm7(*kbe 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 is linq j yrf ,m6+w49qzyc4axge:*b ear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varie. i )r4 kzxl49wkuldh0s as shown in Fig. 6–37. Determine the work done by this f0 dwl kuh4z l9r4kx.i)orce to move 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 acts in thz c- f7p9d f:shhti2o- wi:s)ie $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule, with mass 0yqr:8o iba p9of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubl.b/9u.vrz5j gvq s v:.0rcxh qed, 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 elen7i39l0 f56ngjq7uhbl ogs3 p ctron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar traveling at 105km/h0*b 0qctatpz02 qhv3cg52hus?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose stci pdy-j4 o;4tring exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bowd4p-;c 4otyij?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s nm oa2)3*yglgglove backward 25 cm when the ball is caught. What was the average force exerteg 3y2gl on*am)d by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its minpa asb8v0*,et7 c+uevig6,ug imum braking distance be increased, assuming all else is the same? Ignore the driver’s rs*u e8v e6g+gc bau p0,vta,i7eaction time.

  At an accident scene on a level road, inve d-vnduk )xi ii0pi6;2stigators 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 sli;x udvin02i)6ikdp- ammed 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 the time i0yqq w,c.hzhd4v .pdy 0)9(:i pjvrfot reaches the plate, it may have slowed by 10%. Neglecting,pvqo( y rcqhj9dv.00 df:zh.4p) iw y gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by some5f*p+ vzeh oh9ymtk/3one who does 80.0 J of work on it? Neglect air resistance. zovp y3 t9hkfm+ *eh5/   m

  A 285-kg load is lifted 22.0 m vertically with an acceleurr):1 dz)l-gykkx13 cjx ax2ration by a single cable. Determi)k:r yaxg)zxcur-l121 d kjx3ne
(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/m How m 3f rgl+7 ck23srs+pbvuch must this spring be stretched to store2 krbl3g +7 vfrs+pcs3 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is the bm *m 6f,ro+ mgy9sx+fchange in potg+,ybfr mm+m 6*9sfxo ential energy?    J

  By how much does the gpiofm/:b)c . d qae5c-ravitational potential energy of a 64-kg pole vaulter change if hic5: b q.doef)-apimc/s center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has zx 3it 5f7/1sr lcyto,wi,9ma speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffne1/wctmsit , x7alfyo95ri 3,zss constant of the spring?    N/m

  A 1.60-m tall person lifts a hog/c0d 7sc /uona/-m2.10-kg book from the ground so it is 2.20 m above the ground. What is the po/c ng cd-au/70os/h motential 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 elevjq;g :quj4 1waeog 4l0ation of 1600 m and climbs to the top of a 3300-m peak.a 1egqoj 44w0;julg:q
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically next to a ruler. The end of thhv(qh x edz*;3e 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;hq (dh3e*vz x, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at tgt uj/mhl; 6f-op speed (5.3m/s) and grabs a vine hanging vertic /tl6fh-jmug; ally 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, gmdv z;. c(cc+rq+8yk 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 gcax-d.wr6bp;tm:oq rhs;q5(: / q4nqy u*vujiven a shove up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into gravitationaxehe8c7 ge7: il potential i:7c 8gh xeee7energy without the 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 vertiphu jp -ns7-2pvqer+k2(o/p q cally upward from the top of a platform with a srj (7uo-/k -p2 ph2pqn s+vqpepeed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose spring stiffness constantgcezj*z-s d v :0y6on v)vc9q2 is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward s 9q0)- sc2vn6jzydeo*cg:v vzpeed 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 along the looped trci6,bgb5uyp050w im fack shown in Fig. 6–39. If the yw6mp ii505ubb f0c,g 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 attached to the end of a spring (spring stiffness coqg p5e+1 ./smvbec8i b/osy j7nstant k), Fig. 6–40. The block is given an b7. egy5/s+bmeqs/81 j vp iocinitial 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 jus tatb xns7w ry, h+bg62h.2h7mps from a bridge. She is tied to a bungee cord whose unstre 7+sh2x w2yh abnrg7b.ths,t 6tched length is 12 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 a4 +(cutstr6 oar)+auup to point 1 where it is released from rest. Assuming no friction, calculate the spee)ac6a (rt+o4 ua +surtd at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown witw- a.k:/ bhzyd9sw. wz1lxid5h 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-3aqw9 jfoh )g at the bottom of an elevator shaft. If the e 3)oajq9f h-wglevator 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 the elevator and passengers.

  A cyclist intends to cyclecge3eq w gn36* 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 trav( + 7bc u ka1lbf9dvbv1.nhhm1eling 95km/h in opposite directions, collide head-on and come to rest. How much thermal enkb1l9vmbhu ndh1f .c 7va1 +b(ergy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m highwf. 0bagqki wy(/qkj1*k z73wsy)e 9d and reaches the bottom with a speed of 2.2m/s How much thermal enerk)iyk / 3q wyzk*e b j(wfwa17.g9q0sdgy due to friction was generated in this process?    J

  A ski starts from rest and slides down a * 9mifwarlw rw -9t0x s,dy0.y22 $^{\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 fro uaoki e t2owq z8,r/:e9vf0j7k p/l*um 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 bouzs2d:) by )j-9z b2ooa sbklz3nces back to a height of 1.5 m. zs) 9 bkzyb)ds2:jz ao3ol-b2
(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 q y*g4-r ;edpopulled across a floor with a constant horizontal force of 350 N. For the first 15 m the o4dyr*-eg ;qp floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed of If ztk* j)aj 1fpch8czuw8 .,/b mthe average forceb)8m.jzh wfk1 a8cut/z,* cjp of friction is equal to one-fifth 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 uph-r(ko82qt igward 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 lighkl 8)*okwmo q:,+rhcw t horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noo)kroqh8*ml :wk w+c,ted 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 attached to a very 9w he:fj04lxjg. o:t/ w9vv dflight horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released f9 d 4jo:f0v .jlhvwfe:w9t/xgrom 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 “glider” (mass of 980 kg inclxm sag97 v2*yjuding pilot) that was launched horizontally at 500kmx 27jgv aym9s*/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift al ;r7fsx;xhhh/ew 31s 315-kg piano to a sixth-story windows eh/3xr1 ;fxwhl7sh; 16.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h *h1d-7 6+s lrtobxbbt xhopkx ++o) h6what must be the average force exerted on the car due to fric+hbhlxt o+o6t6x- 1 *kb+7r)d ohbp xstion and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. Whatwvmf80 c,+w7a u j o1dbh4ohg- is the average power delivered by thh 1mh-gwfa7b8uj+0 doo,cv 4we engine?$\approx$    hp

  (a) Show that one Britiq /sh )nw:gp9qsh 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 “kilowatt-) qrmyah9zz ),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 a3mvtd qw.u)b x*45er to 65km/h in about 6.0 s on the level when it is in neutral. A5 bx4v.3r)quedw a*tmpproximately 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 motor do in 1.0 hsa p4y3ga rvlso61 1,ka1wdk6? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If t+j xhv(3euia. his motion takes 1.5 s, what average power w+eu3( aj.hxvias developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through htl- h9qk df oa6,q-w.a height of 3.60 m. What output rk.-6 qod,lh9 -fqwahtating (watts) should the pump motor have?    W

  During a workout, the football players at St cnko**xa+ 9qcate U. ran up the stadium stairs in 66 s. The stairs are 140 m long* x+a9nqck co* 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 cyclisw b 9zd/9psf nu7xf4q)t 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 power output oxal+6s,7dnj / gph,q of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forces add up to 650/qs,l p6+odx,jh 7agn N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg 9w,9p/rxw0n43 xs qjd mayi;h box along a level floor at a speed of 1.2m/sx 3aq sp94/njd, w90xmwri;hy if the coefficient of friction is 0.45?    hp

  A bicyclist coasts d6: va3bs3h,qzchjir,p; z dq6own 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) bu,ny9f br br v*h7e,hd4mpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper bvhfbehn*4r dybr79 ,,e, 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 yl w: lxf(:yc0first 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 1lyly: wfc(0: x.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 floor to start? $\approx$    J

  A film of Jesse Owens’s famous long juo6u6 e;jg,dn 1qav6*l0r zzdqe(1 s xbkq f2p9mp (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need atzqe1p ;kv lx0261gq,s 96deqzo *nudafjb(r6 launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding withou gj6s rif (ng0ph2*2ce+d4ungt friction along the looped track shown in Fig. 6–39 is to remain on the track a60+deirh4n*gc(u2 g gfpj2sn t 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 afterb 7g *ofe 936 pvrbnoiolge.,d*. 6pmi jumping from an aircraft without his parachute opening. He lande f pm 9.e,o7*ogglpo6d.6b *iv3neibrd 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 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 m9h yq k42q.z*fyacein .z-i+rf8 * usother end is fixed (Fig. 6–4. 42efa*i c.ih9r fzuqqnz-8ky+ ysm*3).
(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 made9c2td/te pq6 k in 5.0 h starting at an elevation of 2300 m. Calculate etp96d2qtk /c
(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 above a h7 73e feb(kfxons 5tl/u2l z9auge 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 thao;4ws,pp o +xi. *f pcke:4c 9wqwvnm0t its lifts can move 47,000 people c:p+.wmxe p4owos;qwk0 *4 i vfn9,pc per 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 d r6 su-v.2slae t9boi)am at the rate of 650kg/s and falls vertically 81 m before striking the turbine blades. Calculasu6l. b 9i-tosre) va2te
(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 j-;pt,un(kst, a rk1a–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that isu-a (p, ttn;ra,jks1k, 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 directlyyz yjhu. dv0o38w .*gx into work, how high could an 82-kg man climb a ladder if heuo y*yj. v wzdxg0h8.3 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 atw01nzs d8ged;,pkwm0 an upward angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside tga.-. nupf nm9ekk9.cfe dgf kd3nduu1766o:he scale compresses 0.60 mm, and it tells you your weight is 79u n3k-:mkdndd.67p6. kocf1af fn9euggu.e 10 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a lake (tpqju: g-d : uvhvd 5i/w-b7o(Fig. 6–45). He releases the rwg -p-jbuo(d 7idu /:vv:t5hq ope 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 climp/sig or1-n c2bs a vertical distance of 5.0 m in 9.0 s. What m nc/giro-s2p1inimum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pny15ptx bmbbv0ij. 9 qj *2m/jumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120mix5*p t . b2jj1 vyn0bbm9j/q-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 cu.zog4zpl )b: (+j ;maxe/kxp,(boi f dt in half. What is the spring stiffness constant for each of the twob/m4)jp. ( i xzxl(bf ;ke+g:o,azdpo resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a r/q4u, 6/zr z*x-zd 5 sqkwsaymough 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 accelerate7p8og g*e tcd. -qx hj.cy0jl/ 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 stays the same, and neglect /dyjq.g8 xc * pjto7gchl.-e0 frictional losses.    s

  In a common test for cardiacrn tra n;8s.f+ function (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the powerr.as8;n +tr nf 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-kggwww*bg z41:ze+4es c rock vertically upward a distance of 500 m, what was i z: 4s e+*gwwbgc4ze1wts velocity when it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a rate of 95kg/r,i u)b8l,tq ss (a) If this water wheel is set up to utlqirsb8,), 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