In what ways is the word “work” as used o7-,w*hj nh0u- mi b6bndzlw2; mkqggxs)h25 in everyday language the same as that defined in physics? In what ways is it differenbs kznl huw-hjd*m,x;w5o0gg )h62bn miq 7 2-t? Give examples of both.

Can a centripetal force evetqb9b)h yh/owgam2+y7h1h )er do work on an object? Explain.

Can the normal force on an object evel+iwl5z*.8 .oj zr yj ,fhr505uvfxwet .o+efr do work? Explain.

A woman swimming upstream is not moving withb nyzyl3r/i py9a,3)9z/hu w1n)suygq dg3 .j respect to the shore. Is she doing any work? If she stops swimming and merely floats, is work done on heqsl, hwi n/ ug.3dz9yjbg 3a))3yn9y u/yzrp1r?

Is the work done by kinetic friction forces always negative? [Hint: zl)2o.) s9k y gial3ytConsider what happens to the dishes when you pull yy3)asig tz. ll) 9ok2a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you are doing ln re4(2cwlz.no workrnl2 4l( wcez.?

You have two springs that are identical except that spring :yi0myb; socsg4h 6wa4a l9;3bf ,sxmn3aiv- l is stiffer than spring 2 644s9bihyxnsmcyfbw;0g s3i - v: l3ma,aa ;o$(k_1>k_2).$ 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 thailtup sc+ p91kglz b p)la. .+/vn0.dxt is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it .up.kn.sg+1xpzbtc )i9l /dvp + 0allhas 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 muchkz dwd+dv mss1/ ho31) does your gravitational potential energy change when you jump as high as yoo+hmz1w s dsd1dk 3)/vu can?

In Fig. 6–31, water balloons are tossq;,wxkvwlh, 9oa +c)zed from the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impact? Ignore air resist 9,wkh w,v+;z coxalq)ance.

A pendulum is launched from a point that is a height h above its lowest point )o4ymyp wk2r7*l+ (m2pi pq4qci/o voin 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 swing the largest ango oil+ 2q /y*wcpm( pv rypmik2o44q)7le from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If d z)dhgz76d2 nyou compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the la27dz)6gd h zdnw of conservation of energy.

A bowling ball is hung from the ceiling by a steel wid ex*jrre9 5xyp m0o7(re (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 ie0 jr7rxm5pxeyo(9 *d s supposed to release the ball without pushing it. Why?

What happens to the gravitational nu zpz2anh,. 8+dbct 1potential energy when water at the top of a waterfall falls to theuzbdz1,n2pt+ 8 ca n.h pool below?

Describe the energy transformations when a03st6 48.ojeewq zz kb child hops around on a pogo stick.

Describe the energy transf:9sq.pk* ofbse7yob4 k n +,eaormations that take place when a skier starts skiing down a hill, but ae: kb94+ss.o ybn7okf *p ,eqafter a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of i; /3aj :6qq* lpkzen*9d nspfp8c,usa hill of height h and slip 8s/3jn* i;d*qpfuq,slke cp9a:n6zdes down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step oiaaol 6lm :hc qcg:e )q1sfl/r7lhx 0+;;8uoover a fallen log in their path rather than stepping on top ila0oo;/c r sqhl7)6u ox8afq;:h :l1m+legcand jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the other, are fired id9c;x ozeo: r l/d5g6fnto a bale ofdoro9 le;cx6f/:gz 5d 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 fz16dn x nd*k,swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into acxnf*, n1dkzd 6count. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greate gp bmi.a05o;yan.o8t r than its originai5pao oy agbt;8n.m0 .l height? Explain.

Suppose you lift a suitcase from the floor to c( tc(j (.va3m ;ynnkja 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 s (jkny.vc(j;mct3a( nuitcase?

Repeat Question 22 f vn)lorkv;v+o kv02 0jg*j4k dor the power needed rather than the work.

Why is it easier to climb a mn ln k9f-:x;bsountain via a zigzag trail than to climb straight uf-kxn;sbnl :9p?

Recall from Chapter 4, Example 4xr a .jrykzxf:8 i*/4s–14, 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 much rope must be pulled up? Account for this, using energy concepts. : yrjr8/sxax*f4z .ik

  How much work is done by the gravitational force when a 265-kg pile drive eirc ;g1g yzvauy6.( cpj )6tr(+y-rxr falls (y1+va (;y t6 ijrcrzg6rg .exuyc- )p2.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much woe+47p ;wmb.z zbp8cjkrk is required 8cpmk74.wje+bbzz; p ?    J

  A 1300-N crate rests on the floor. H7t-2tw bwcfj av*h,/ gow much work is required to move it at constant spevfc7,/*w-twg ja h t2bed (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 cx kn/av2.non2y-lpth,5kiz 9o:p f g/rate 10.3 m across a rough floor witzgtfknxi 92:avhln.p 2-o y p,k5on //hout acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is acceleratepeb68qi2rbs8d 7r6h nd by a force across a floor at a rate of for 7.0 s. Find the ne8dr i6 n e2bbs7qhr68pt work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. How m(uivez*. ol i:(f zk-xuch work is required t:k e* o iuiz-l.vz(fx(o stack them one on top of another?    J

A lever such as that shown jaei 4ux7ivg8*s 3pt/ x- x(iwin Fig. 6-35 can be used to liff objects we might not otherwise be able to liff/wp-(stj 3xi4uig* i 8x xea7v. 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 kept from acceleratincblyw* m , f- -po;vtpb9.a,crg by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic *; c,wlvt- b o f.m9prybc,ap-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 ac8tx.w)s,u c 2lnh7 czr i5g4qdceleration of 0.1cdl nht)q5 r.c8xgi u7,2zw4s0 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 tcmc)90wz fg, the distance axis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as shown in Fig. 6–37.x mbc:nf7 u8cxj( 7wel;:aw+x.z9wc w Determine the work done by thicx:7bxwj7c:9cm(fu;8 lx .wwn+wza e s force 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 tz/wj2kis1 nb 37-2olv*mc xgvhe $+x$ 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 zqm-ldu f t307sy8 0jbmolecule, 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, byh8xpcn+a4-csh yqe7qly- d6mf3 ch: , 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 stop3 wu z)njuxl0, an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar traveling at 4elh.z7o3 jmx105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from r(yigl y09:g la bow whose string 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 lgly0y:g9r (i leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25 cm whefbv/2j4n rcz 8es)/nen enjebcv z2rf/8/)ns4the ball is caught. What was the average force exerted by the ball on the glove?    N

If the speed of a camv3pcervb. 3+3 r8rlv r is increased by 50%, by what factor will its minimum braking err .mc 38v3+3 pvrlvbdistance be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s skid mark8 v2yb)i0ysyqb ,7 4rnt l/oet to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked)8b2/yye l,) rqo7 i0ybt nvt4s the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is gs)l2m*) f/7nbxxutz9 p7 zhbpitched at By the time it reaches the plate, it may have s zzpfnt xg9)7s*)b2lu h7 bmx/lowed by 10%. Neglecting 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 soulg9t t3qdq80 xl(zazq2) p9n meone who does 80.0 J of work on it? Neglect air resistancu(8qtd)gq 3 la0tlnqp zx29z9e.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a s x9gtqt et 7nqj1/mst-n27zx9nx30pbingle cable. Determine tn/09t9 bnx jspxzqq73 2ge-1x nmtt7
(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 much must this spri* 4:lkal4nrgbofc 3 m-g4ow0 u5 smw2dng be stretched to store 25 J of potential ec lf sm-rg 2g5*md40ao4lwbuw: ok 4n3nergy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is the cha twlr z(3u(4vxn(wz4lr(3 vxutge in potential energy?    J

  By how much does the gravitational potential energy of a 64-kg pole vaulter ch5a1nfskn6 4 2i1zz fvcange if his center of mass rises about 4.0 m during the jump? snv5za z4i 612kn1ffc    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 kma,dw i4.ie0iz /h when it strikes a horizontal coiled spring and is brought to res,40 iai ez.wdit in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so b.2 tepm6;5ts ixbct(it is 2.20 m above theb2i psb6t cxt(t5;. em ground. What is the potential 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 8fbdwy 3s,9tm i4xzo :j7om/ jat an elevation of 1600 m and climbs to the top of a 3300-m peak. /ms o 8xf4w,myjdtj93:zo7i b
(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 ver 5qzzw )vg8qpw+g7v x-pn 6o:fwp p.y.tically next to a ruler. The end of the spring isp8no gq 6) p- p7wx:+qgvw ..yzpwzfv5 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 ruler marks?    cm

  Jane, looking for Tarzan, is 4b plg)iw2/ b-i8bvg)qcva+st3zx4xrunning at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing 8-qtx+ic4ls)vp z 4 )g bv23ibbwax/gupward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting fromtt1/-)u gkqdj/er 3kp rest, slides down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a f0jltc.v1d3my hm oa4jbe.; 1nrictionless 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 k-xa 0r39axp ieinetic energy is transformed into gravitational potential energy without the aid of3ir xpe-9a0ax 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 the top of a hcc6c9az s(g 5platform witgc (szh56 a9cch 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), whose spring stiffness constant is 950N/(u20ek szv o6dm is attached to a table and is compressed down 0.150 m. (a) What upward speed can it giveeozv (ud s6k02 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 track shown i;yrd fckk i6x4yxe e :b:e08xl4bbg6dm4+0tyn 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 height4ex d: 0e846yke4fxb0 ;ybl ycgird6m+kb: tx h must it be released?    r

A block of mass m is attached c8truy8z1du(ql ;nwr0(o- /v sbx 6iuto the end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial displaceme c6 yunu(bduzx 8q(iw1-;lr sot r/v80nt $x_0$ 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 a bungee cord v bcwo8un95h/;p dfdv vy38n8whose unstretched length ispyd /vvu8cf8 895nh ;nob3vwd 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 up to point rvm:j3s (zi4 c1 where it is released from rest. Assuming no friction, calculate 4v3sc im jrz:(the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a spee- hsp r( e)okvoe6o:s,d 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 elevator1z d;;m1d.zu wo2 .lfxil)qxe 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 broug mlzx1 ew. f d2oli.q1u)x;;zdht to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to9 **kx;s7 qkyn *flitqxp m0l7 t1oxb: cycle 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 traveling 95km/h in opwtc 2xd15d56hf)d w2 n-f vnylp -/ykpposite directions, collide head-on 5wl p wn--/ffv p2 tk6)xdd21nchdyy5 and come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reach dvb:mu)2+xq+ efr iqn+( o3nres the bottom with a speed of 2.2m/s How much thermamn+xrd+(fvo) ir qq :+3u ne2bl energy due to friction was generated in this process?    J

  A ski starts from rest and slides (jwe:3b79 xrxv,nn cv 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 groun 5qwl,(6nhmv eu ;becd1y fu53d.
(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 oj, +atgx- 9ghdf 2.0 m, and it bounces back to a height of 1.5 mhx-jg,d+t 9g a.
(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 reln hl2rywu8z c5x 825rst, is pulled across a floor with a constant horizontal force of 350 N. For the first 15rxw 5cy258l82u zhlnr m the 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+/ s1vt mw ej)lfb28kt of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. /)t jt+f2mwb1l v ske8$\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady upwar 2k;c 9bp1zq ,bb ic1/njnj6kzd 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 lightpypt,)ydl9r 0 horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stoppinr0 pd tyl9),pyg 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 light horizontal spsj3vt*p;j4 alring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretj4p3*vlja t; sch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 kg in8fv k2 t0t6v(vlz3 cejcluding pilot) that was launched horizontal (vk vfjv 2lt860ctz3ely at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a sixth-story wiemxwk,r4 fc 1)91c0rsum j3uundow 16.0 f )x0u1mcc4 jr1umw93kseru ,m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must jo g04*bbb9jow 5pi+pbe the average force exerted9*0j o+5p bwgob4jbip on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h 3lu 3w+ e fzf3jp219qrsldg)qin 7.4 s. What is the average power deli9q zrsdlq2lw pf3fu13 +)g ej3vered by the engine?$\approx$    hp

  (a) Show that one British horsepow svt jv23rs m s.sg,u0jx;,h,yer$ \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 o*xli4-y l)*u5m r iyucf “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to dg83(( neok )ankc h9j65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 3g)8 o9aekn(jhk(nd c75km/h.    hp

  How much work can a 3.0-hp motor do in 1.0 djlqg a pi6n6zu x8.b, ;kjij1a:a: l4h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this motio+pf5xhu -xh;in takes 1.5u pxi-x5hfh+; s, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per mzr :4/hmh9 fxqinute through a height of 3.60 m. What output rating (watts) should the pump motor ha9z/mh:qhx4f rve?    W

  During a workout, the football players at State U. ran up the stadium stairs in o3ryewe9v0s1ks3:sq p9wk(gb2d-k f 66 s. 03rewsoqkk9: k p-ysd2e1wfb 3sgv(9 The stairs are 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 cyclist climb a 6.0l.*qn f6*iv;num,lo w, u0dkep0ow*f $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 12 s9ute ./m.cmd0vcj; f0 hp. How steep a hill can it climb at a const.stufjcc 9/e d0m;m. vant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor havx ;b+a n74upxve to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coeffiu b+ ;7ax4pnxvcient of friction is 0.45?    hp

  A bicyclist coasts down a 7.e 0ujj qh-80 6z96col tmhtde-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(89f m0gnpi .p/ 7xha h:xm9 )cdkeuu,c9km/h) bumpers” that are designed to comprnp)m xiu99cp.cd,0 / mhhuf :ge9a7kxess 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 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 firs( 5g 3,pf0tsy6 p fg (:(eykg du8e3gchp+edwqt shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average ffsc y 635 ddpg8ueg ,gwe gh0(yqtpe(3k(+p: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 famou qa5uvi1yqs9uir (u of l9f;23s long jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from laun19qf iv2 asrl9u 5qfyuu;i3o(ch 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 sliding without friction along the looped track shownvp78gn dnczd f1m f/p: jlk57( in Fig.dp:vjgmk1d nfl78 /z5p f(cn7 6–39 is to remain on the track at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an airgh7 et)jr+vq0 craft without his 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 kgq rt7+ e)vhj0g 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 oi:w urw9ga2.fj3qo 3re23+;cnh jft vther end is fixed (Fig. 6–43).fawj2t9 i: 3qwrgj3+ o3.eu;cnfv2rh
(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 gatn276lqb d uva i md3zppzxa2.;7,7of a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation o b a2ia2nxm ppv,d36 7dtu7gqal.z;z7f 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 wngl4 ;;z,pt1rae n ;jnhen 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 47,0j(bu- di i1v1ho;g :fw00 people per hour. If the average lift carries people about 200 m (verbv1hi:(-wof1;i g ud jtically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dama)xz p2o*xh.s at the rate of 650kg/s and falls vertically 81 m before striking the turbine blades. Calculatax.ox)h*2 sp ze
(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 v8bn,+1 ag6e) efdeanpertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as yourebf8 a,na)pn 1+6dgee 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 cany-(;lxmz qobt* k3qx 4dy bar directly into work, how high could an 82-kg mqzl(43ky- tx *oqbxm;an climb a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fireyw6 amc6.z4d tsgx+r. gc8r4c d at 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 bathroms/jz/0 291ll *b,, ucdgwzj*th ignpom scale, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?g gzu,,mdi0b*hjpnz92t*l/1wsc j/ l    N

  A 65-kg student runs at 5m/s grabs52sqo:0v)fbp hprw* ni()n sx a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his veloiop :p2bf )vx5sn s) *(rqh0wncity 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 athbk u8 atvyz, ( hl9(i,vxp1s-fsnw3 *slete climbs a vertical distance of 5.0 m in 9.0 s. Whashf31p9v(,zn-kx 8ub, w* yalivs (stt minimum power output was used to accomplish this feat?    W

  Some electric-power comtzp m30 iepk xdvl-3*c057vdapanies use water to store energy. Water is pumped by reversible turb-3 dxk0v t pizvdc5e3ml* 7pa0ine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in half. What is theczn6 ymy )j4b0 spring stiffnec04yjymzn 6)b ss constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rojg58s dxudr1w 9n3 zw3ugh 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 from 35km/h to 55km/h inhfy.*31l0ty +m ozhi h 3.2 s, how long will it take to accelerate from 55kml 0yizhyoh3hm t+* 1f./h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac k3o /xnfgn 5:a*9ic sefunction (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmcn3a: kx*5ine/f9sog ill 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 verticwcyd-f ;m(rh1 ally upward a distance of 500 m, what was its velocit w;-f1d h(rycmy 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 mx(m8 shpd:9zs n0(u l8ts tog8 at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what sgx: 0op9(sths8 ( u8tm8nz ldis its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s