In what ways is the word “work” as used in everyday language the3ipleu 0k2pv)f 6/l do same as that defined in physics? In what ways is it different? /ev ip duolf k203pl)6Give examples of both.

Can a centripetal force ever5 wqlwy9exzp2i+8 8 pi do work on an object? Explain.

Can the normal force on an object( hsot h;(k;e-zyyix4vv( (gm ever do work? Explain.

A woman swimming upstream is not momymg5;g* .0drswc p.o ving with respect to the shore. Is she doing any worsm.*pyg c 0g. o;rm5wdk? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic frictm88u u.ln)i*/l wqbm gion forces always negative? [Hint: Consider what happens to the dishes when you p8blg u ni m)/u8*w.mqlull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall uq w1nk)f6 w1 ywkp+v4even though you are doing no work?16)kwk4w nwf yq+vpu1

You have two springs that are identicalhxc csekf/2 +.e /kkky5t+-gg except that spring l is stiffer than spri/k+x f5.ec/shtcggkkk2 -ey+ng 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 horizot.h3sr 0 akw0ge3,ee fko/iw /ntal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time oewe3sk trag/ w h3f.,eki/00it 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 gravcm *f*s32dq *) ulhccxitational potential energy change when you jump as high as you2q*c*cdhxu3 *s )mcfl can?

In Fig. 6–31, water balloons are tossed pl)s4i .c,:;l/p1hxl n (es obv3ovgck ik8h 7from the roof of a building, all with the same speed but with different launch angles. Which one h v bcp7/v8sg k;3i.e,h( loni):l4 olxhksp1cas the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lower8 e0.gvgem o.u gmt(:st point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swivr. u8(0 oge:tm.gem gng the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress th(fu.5 s-h :nv ;gbgcdle spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservati sd un.c5l-bgfg;(vh:on of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). nda8xrwa w 5)l.f9js bpa))9a The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed t)9)wp8) an5lbxr.w9f asd jaao release the ball without pushing it. Why?

What happens to the gravitational potential energy when water atg rdt/9z 12euq the top of a waterfall fallsd921/ gzue qtr to the pool below?

Describe the energy transformations when a child /5-ej5q uq aufhops around on a pogo stick.

Describe the energy transformations ts/b,/a w b7roodaq* j+i..hbrhat take place when a skier starts skiing down a hill, but after a time is brought to rest by striking a snowa/o.ad w .j/h7rqo*+,rbbisb drift.

A child on a sled (totalgq2 ea(y-y 53nbklw0u w6p 7:exrvkw, mass m) starts from rest at the top of a hill of height h and slides do7vwnk kybpguq2 ywe03- : 6(xear5l ,wwn. 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 -qg,ca84fgi8 rdn-bp step over a fallen log in their path rather than stepping on top and jumping down on thed 8af4icbrpngg8-- q, other side. Explain.

Two identical arrows, one with twice the speed of the other, are fi, 7/f0fvdbbrb 23wkvired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will pek 7r20 fibdfv w,bv3b/netrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in t:yo (u 2 oz0wzqgvmdp-ia:-lz;- -j9ljaun2 werms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clom la0; ov wow-zj d-i-u(lquzg- j9z:22:nya pck has to be wound up.

When a “superball” is dropped, can it rebound to ats 07); 07xf-gym8lyz i9d0d ktflgdy height greater than its original height? Explai 7tlm gkdi07t-8g ds0y;lxfd9z)f 0yyn.

Suppose you lift a suitcase from the flr2a86tl0 hnn koj y1i)oor 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, (nio aj0k12ln) 8htry6c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for qs ok,yf2fkn1i45s 6w the power needed rather than the work.

Why is it easier to climb a mounsqeti1+ h8u/q zy:v y1tain via a zigzag trail than to climb straight uq8y:e1izhvus +qty1 / p?

Recall from Chapter 4, Example 4–14, thstw;fp i:;, vnat 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 enw ,v;pt :sif;nergy concepts.

  How much work is done by the gravitational force when a 265-kg pile dzd+3g9r cuhlnc,3f+c02 ko vgriver falls 2.80 h9 ,g uczc 3k+3clg+vfno0rd2m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much worm*l /f(d zx(-ml.sn syk is requiredz(.dlsnf* /- mymsx (l?    J

  A 1300-N crate rests on the floor. How much work is reo-9v9fn*we,+ 1zks wl n)-o5o rq mrbjquired to move it at constant speed (a) 4.0 m along the flvnb kw1,s9 m-q)lzw-ofron+* e9ro5 joor 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- 5;k o a-pzv6.gsoiwb crate 10.3 m across a rough floor without acceleration, if the effective coefficient of frictios56 oib. owgav-pzk;-n was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a +6 :9cdvlyy*. hy:8oe+qfx*dcsbndn floor at a rate of for 7.0 s. Find the net work do:e9on x db cf*h6n8* cqylysd+.vy:+dne on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on;h( w fnyqj6b6 a table. How much work is required tjhqbfy ;(w6 6no stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to lifo8ov u) -tc)k9ufayf9f objects we might not otherwise be able to liff. Show that the rato)fu) f 9 a9ukc-vyt8oio 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 slide6d 8kddcfrz+ 1s 3.6 m down 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 coefficient of kinetic friction is 0.40. Calcdrd8czd+ 61kfulate:
(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 kn ufgzo/7tk ,*xs +/gu q/t5lof mass M an acceleration of 0.10 g upward. k*// g5tz7oufglq /tuks + nx,   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 isc 8m0s4uddq ,1 :tpmxzqme39b 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 Fi+,xcyvkoeo 6sl9w+-q-di h t*g. 6–37. Determine the work done by this force to mov kol 9 td+q-s*ow+h,6xvciye-e the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

  A spring has $k=88$ N/m. Use a graph to determine the work needed to stretch it from $x=3.8$ cm to
$x=5.8$cm, where $x$ is the displacement from its unstretched length    J

  The net force exerted on a particle acts in l2d/t2 i12dx,dntgn sthe $+x$ 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 hgua ok2o(73gof $5.31\times10^{-26}$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 i3c,xect dq q73ts speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is requi+im .gyxi6:t b kuoz3,9owh zr/*q:d pred 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-kgcar travel1zdy+:8 uwhz g(k p*ccing at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired f dg/,qp:+yl- h fj9.u6tzyv uirom a bow whose string exerts an average force of 110 N on theylj yvt /uug+hd:i9f,. -p6 zq arrow over 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 fielder’s glove backw7n (/zg*dmhud0ac nc z*o02 wvard 25 cm when the ball is caught. What was the average fc oh/0z 0gd2v w*cu dnzam(7*norce exerted by the ball on the glove?    N

If the speed of a car is c9wt p gd0:m1dincreased by 50%, by what factor will its minimum braking distance be increased, assp9 g0w cmdd:t1uming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, inve0 ezuyzf,:n(k i*veo4stigators measure a car’s skid mark to be 88 m long. Theeunek *f0(vz 4 z,:oyi accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass ofl9m.6f 6vyfh*tuff0 d 0.25 kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force t.9fm y6ful f6d0f*vh 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 8h exb01tr- m twqe3q6up by someone who does 80.0 J of work on it? Neglec1qerew3-t0hb 6mxt8 qt air resistance.    m

  A 285-kg load is lifted 22.0 4jm./ *a1j jt,fgkdgdm vertically with an acceleration by a single cable. Determine tk1j/j.d,m a*f4 gj dg
(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 ststg ff 5jao1d ,99wn::ewi 3aaiffness constant, k, of 440N/m How much must this spring be stretched to store 25 J of potenti9inj 39::,f sawa15toeagdf wal energy?    m

  A 7.0-kg monkey swings9x6 0sx /qmu icws+x;h from one branch to another 1.2 m higher. What is the chani6hx ssxmu9c/+;qw0 x ge in potential energy?    J

  By how much does the gravitational po ;a0cde k/ :wqa7hun-wo3 cl0ktential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m duriww3nqkkd/ha;0 a:uc 0leoc -7ng the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h when it stk 0esqk:w2vsm-: 2 ltvrikes a horizontal coiled spring and is brought to rest in a di2ms 0kw: sltv v2:-qkestance 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 4pat mn sb2us5+en.e. the ground so it is 2.20 m above the ground. What is the potential energy of the book relative to tn+2es mpbs4.a5.eu n
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and cl :6fmn 0h(asymimbs to the top of a 3300-m peak.0y6mf :sh(ma n
(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 ha.+c aafeu+e ;zngs vertically next to a ruler. 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 eazac;ef+u.+will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) andlenwbx y33.2l grabs a vine hanging vertically from a tall tree in the jungle. How high can she l l23 ne.x3ybwswing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting fromoike+o014 p0zej69 qntasv+ j 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 frf/ns0b 3l 5 +dbcvcl5nictionless 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 transformeyuepv*1 z; k- esas8:gvcf80wd into gravitational potential energy without the aid of a pole. Wit w8 svfesuce;p a-y vg08kz*:1h 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 upwar. zx.9y*h2ri dumse)sd from the top of a platform with a spr)s2.hdm*zusyix. e 9 eed 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 (ignore4 iub v.f vz0k.usqb;: its mass), whose spring stiffness constant is 950N/m is attached to a table andbzq4uf:i .kvvb. 0us; 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 along the looped track show:crg )nk4oq9nn in Fig. 6–39. If the block is to remain on the track, even at the top of the c)cgqn: o94knr ircle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end w ic 441*p/ccihkmq7s/j(uh vof a spring (spring stiffness constant k)cuh7vi/kmc1/hw4pj 4 i( *qcs , Fig. 6–40. The block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungee cor/91i-ydk8s vz,mr m ckd whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s lawdk/zkc-sm8mv 1r, i 9y applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster ci8n ngm)b afk+x; t /ey53 v0w(zxhd5har shown in Fig. 6–41 is dragged up to point 1 where it is released from rest. Assumingxe5n30dk h) z8vx fbi /a+(tynh;w gm5 no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12xv:q bax1w 6w5 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 be53klop bji x gewhm9hj,cdz2,d.r(p2 *0f1 h ottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the s.xh2 0f2m3d9,ep1(jrp zcw del*kh g5hbo i, jpring, 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 cycle tptn1mkom79/ -xslp j6-r;m xb+d5pe 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, eachn2 /ekpwtxu5 *dx(ue . tx14ue of mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this colliueex 5/ * d1(x4tweun kxp.t2usion? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom9w zk3+/f4yz jc(x cal with a speed of 2.c( +y3jca/zzf4 wk9xl2m/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides downssp/7 2qo3 ouz 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 a .i 1,5 xorym0.r ni)vptxy+8,bzetzobove 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)wgu lus1p g2p0noz pe4kk,7; a height of 2.0 m, and it bounces back to a height of 1.5 m. ;g ,pp1z2 lk eou w)n7gu04kps
(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, izvu xb672r9q2g 6oqzzx, z0ux s pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, anxgx02 u bo7zvr,2xu966 qzzqzd 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 Ify 9)4 3 merle)nwgeow;-spp(s the p9lweepr3wm(g)s o) 4eysn- ;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. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a stu guyz prjdd.yp5q;z2 l4 3xry/ 47e1teady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light h4/ xlza4mg2 kzr+f d(korizontal 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 eqgma42rxklz/ +( d4k zfuilibrium 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 attachev2a 4cgftal4r6 s9,mc d 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. If the spring is released from this position, how far beyond its equilimsca6,c lv 24t4f gr9abrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 kg iazu7 e-/wo3 sayf(ez- qv-o0fn+ei.nncluding pilot) that was launched horizontaeo n0ie-3qnau.z--vw( / es7f+zoay f lly 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-storymmqv8jbh9 64h z gf+wg r-6ng6 window 16.0 48 z jvhh6rmn m-qgf+6g 9gw6bm above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must t0r.2cao 9ls dbe the average force exl 0ra9so2tc. derted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates fromb.k;p;zba x) r rest to 95km/h in 7.4 s. What is the averag; xkab)bp r;z.e power delivered by the engine?$\approx$    hp

  (a) Show that one British horsez8 8ho3*8km qw kccg 9umgd;/5qhu(tu power$ \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 )ekue8gc()(.2kk c jl ug;iqg often expressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows dowrz) y.b i o.nq2/px7tsn from to 65km/h in about 6.0 s on the level when it is in .)7o2sxtpyrzbn/ i. q neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motok:*q*omx:8mop +ge rpr do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If tqe1 cr8z zw6 56yqqm7ohis motion takes 1.5 s, what average power w w c q6875zeqmy6roq1zas developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60*7pe1cr c kyd c7b8ug*wavo 94s,tkl7 m. What output rating (watts) should thv*dp1as*kly4cg w7 9 kc, 7oruce8 b7te pump motor have?    W

  During a workout, the football players at S7 *+f 6+e nvax9bj.4 jx-jfhgwwyanj4 tate U. ran up the stadium stairs in 66 4bj j6w*.nn9f -w7+ ahya4xxf +jejgvs. 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 clin cn 4uros; a32dhr1e(mb 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 of 120 hp. How steep a1iroxqc ,7dm :mq3-iz hill can it climb at ao13z ,:m cdimqxi7 q-r constant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepowdc6ns0+(z zfx6ww ut +er must a motor have to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient +6cx(w0nzz sfu 6t+w dof friction is 0.45?    hp

  A bicyclist coasts down a 7.0 l/j*pelq 9ro a*sy8u:$^{\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 buizkkm t,((bi*mfu/ qi*lt “5mi/h(8km/h) bumpers” 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 be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wb(mi tku*( z,qm*ifk/all? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the grjzu c am*0na0/4t4xfubj/(zj ound, and the remaining four she0*f ju 4zucba n(a //04tjxmjzlves 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 floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Oe.mzpvyusi l (dx1 r0vo.7q:/lympics 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 if su. /(7zxlrmvvq.y:0pe d1 oi he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friw+6t sh8 v:w jse: wi5dm1)hliction along the looped track shown in Fig. 6–39 is to r+mj:5sh w: dth6wli1v )8wei semain 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 aircraft without his o du11:zm,p. ghq*ae qparachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass w1dpme :qa.o* qhug z,1as 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 alo0 j9/ej*pwf3y 69gb kql9vn horizontal cord of length L whose other end is fixed (Fig. 6wvpfkqy6ojbljl9g9n30 e / 9* –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 clim3j jzr6 :bj f.e.6tnmgb is made in 5.0 h starting at g:rj6.3bt j6mne z.fjan elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 vx vf0+l9 4d 7p3l 4nkshuwdw2*pr-slrb 7sf1 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 tuq7 q/4pj1ovd ei5n* dhat its lifts can move 47,000 people per hour. If the average lift cvd7jo/i qp4n51due q*arries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls verticallyek9y (g(e9q df 81 m before strikinqe(9k(yeg9 f dg the turbine 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 withil1+wxiy0 k. s a circular vertical loop (Fig. 6–44), the difference in your apparent weight at thely. k1is0ixw+ 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 cj2 5cs; w lv6vwrgsqn (4mfkz+vw./ua ls0k. )onvert a candy bar directly into work, how high could an 82w/ jn0+v k564r.fvaw2qgsu.zw)s ck;(mllv s-kg man 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 fired at an upward angle of 45:p4 fgj 8iz azl)-x4zn.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, the8h-bq w4mgb nqu9mc/q7kk3d / spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if y g/bb nkm98k d/3hqm4ucqw7q-ou 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 swin- n5cas8c swwbp y-39xl7*icogs out over a lake (Fig. 6–45). He release5s7bn *o-cc- iyslp3w89 xcaw s the rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5.0 m in l/s qef5n- 3di9.0 s. What minimum power output was used to accomplish th5 d3sflq i-/neis feat?    W

  Some electric-power companies use water to store 1blq 2wo;gfx ;tg/w,senergy. Water is pumped by reversible turbine pumps from a low to a high r;g2, /s ;fx lgtww1qboeservoir. 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 biqfh46k g(:t stiffness constant k is cut in half. What is the spring stiffness constant for each of the two res4:k (t 6fbiqghulting springs?   k

  A 6.0-kg block is puu6ysqwdrku.d3 ) k )m7shed 8.0 m up a 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 from 35km/h to 55km/h in 3.(qm e556jzx -z.rmcr h,wj+pl2 s, how long will it take to accelerate jp5(+ mw5.-,hzq 6jr clmxz erfrom 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac fus)ory j; p13hwzvz5 a5nction (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg pazswhv)3oar15 pyj;5 ztient 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 50z2 *y2n0jnwycs+61j cs sp6ih0-kg rock vertically upward a distance of 500 m, what was its velocity when it left the volcanoj shy1 6yc0 wn n*+i226zpjscs? $\approx$    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/s (l2m8)1k tn q/l l2mceta) If this wate1 8ct2k le)t2l lm/nqmr wheel is set up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s