In what ways is the word civ6d4h 5: 7lxdf+o qpbp/ejs/n8 bp0 “work” as used in everyday language the same as that defined in physics? In what ways is it dh d i 7pq56/4ppbl:os +/xfvb80ndjc eifferent? Give examples of both.

Can a centripetal force ever do work on az p8w6 yl))eiz4i tn5me*nl0 an object? Explain.

Can the normal force on an object ever do work? E4.si+amy ju: kh.dz;pk3 4 wqtxplain.

A woman swimming upstream is not moving wikso. w6o (xrgluxw9 kr-)j21 xth respect to the shore. Is she doing any work? If she stops swimming and merely floats, is work done on owr-lg.619rs k)(xojxxk u2w her?

Is the work done by kinetic friction forces always negative? [Hint: Cztr)o , v4i,wdiuiy-6s t;j 7 m,zvuk2onsider what happens to the dishes when you pull a tablecloth out from uy,ksiu2 7i-tr j 4 u,mw 6tivzoz;,vd)nder them.]

Why is it tiring to push ha:y qo kqxeb92)qf*z8wrd against a solid wall even though you are doing no worfq9qe k 8:oq2yb z)x*wk?

You have two springs that are identical except thb//)j/ 5h xiz 4xutxkwat spring l is stiffer than sprin u/ /xwx)4hbi5jt/ xzkg 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 to8gu:q )90 jl+g5ncu9bmenfe-c(v g3 k hgnge0 slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by thkeu u(gegmvfl9+h- ccn 059ggg:jnn)3e0 q8 be 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 ene9zt/z avp;*ky-j-wu+ oju bfkc mm-;1rgy change when you jump as high as you can?jfkm u-c/ -pb +zmwt9k-jv;;y zuo1a*

In Fig. 6–31, water balloons are tossed from the roof of a building, all a/as , dg+re9nwith the g9 ar/en+sd,asame speed but with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lox m t4 2*c/zi/2+nwmmdgtumk /west point in two different ways (Fig. 6–32). During both launches, thk4/t2 2tcx/+/uinmwd zgm *mme 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 angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compc ;cisoo,jm:.q evb2l9 p6lw8aq/pn7 ress the spring by pressing down with yo6v:qeops,ba/2 p.clo;wm9q7nc 8ilj ur 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 (Fig. 6–33). Thpz0:9(: se veytsv g9(uhw/..r yoxht e instructor pulls the ball back and stands against thevv9 (/ you:xry ts :9e.hzt es.g0(hpw wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gra :gf)yih2 *lo. jqe2ufvitational potential energy when water at the top of a waterfall falls to the pool below?2 ihyglfeqo *u).j2:f

Describe the energy transformations whexei+haq/(yx ,5av j;tn a child hops around on a pogo stick.

Describe the energy transformations th ;rt7zjb+kds *at take place when a skier starts skiing down a hill, but after a time is brought to rest by7zt;+ rs dk*bj striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top oatm(* he -a:;rd w*n0awxow1mf a hill of height h and slides down. Does th:m (a1w hr*;- dntxweaa0*mwoe 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 over a aaj(g tr /gv-9fallen log in their path rather than stepping on top ajt ( vgr-9aa/gnd jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the other, are fired into a hv b+lwaay, die87w. 7bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the syawh77v+edia.l 8,wb lower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms o)9zuzo;xz z4ds t,g.rfn ,h5g f energy, (a) ignoring friction, and (b) taking fri gs zh9zzoz4fd rung5)t, ;,.xction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a heigfwfa1ex-nkb29*emm2 ht greater than its original height? Explain.f -efkb9xaew*2 12n mm

Suppose you lift a suitcase from the floor to a table. The work you do haczt6 mt i,s6u29tj- on the suitcase depends on which of the following: (a) whether you lift it straight a-t2z6sh, jc u6tmt9iup or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed ratheo,l+ri+ ybft yxt6. u:jyg j4lh03heoo+g ;7i r than the work.

Why is it easier to climb a mountain via a zigzag trail tha4,+cdxfusu ry3kt2n )fhsp64l ev t 61n to climb straight up6c,+f yls h 41)3utv2dsprtf64 kuxen?

Recall from Chapter 4, Examplei4mki(r9x wn u 7g5kr4 4–14, 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 concepw 9 r7gn5 4mix(ukirk4ts.

  How much work is done by the gravitational force when a 265-kg pile driver fallsy0s 6i5 irqv7syqsv06r75i is 2.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 msk:m3rikkg0k+i2poa nu dj2 wk;.+ :o high. How much work is requi wnaus or+.igmkk:j:kp3+k2 do;k20 ired?    J

  A 1300-N crate rests on the flo o4g24 5ju8pk*8gevz mzjmh e*or. How much work is required to move it at constant speeejm4g ju88gpz hko5z m4 v**2ed (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 (horizontal1mhv+wza ;vi5*k i vu7ly) pushing a 160-kg crate 10.3 m across a rough floor without accelz *iik hvavv5u1w+7 ;meration, 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 at a h3xc7f:-nk w erate of for 7.0 s. Find the net work done on the box. h cw :fk3ne-7x  J

  Eight books, each 4.3 cm 1))p l9zp4v,kp g8qi o gvdh(lthick with mass 1.7 kg, lie flat on a table. How much work is requi8v1piz) 9o,h dqgklvlg)p(4 pred to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff ob 6q (g6l 7vkeugr1yb f3/dholdod 4:x2*q7tq xjects we might not otherwis3 b(x:tqe1rhvoqo*u / kdgq 7f 67dg2y6ll 4xde be able to liff. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kept frsuji(sf;mha*4 o)g5xf1h sr: om accelerating by a man who isojs()4:fxms gihf1a5r ;u*h s 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 helicoc4(px1gnzy ) m 0tve;hpter of mass M an acceleration of 0.14hn tyz1c (m0e);vgxp0 g upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume the distance axis is l6 bv8*cb z*jwbinear 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 axu,ks xq rn.r;u80g9u gis, varies as shown in Fig. 6–37. Determine the work done r r gku,.908sxgun;u qby this 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 actb3ihz m4ryru7 m7a 6,rs in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule, with m x/ytulso1+rwacq;;42,z: ii: ed .mcgqe;jmass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has its speed increyiy zgj (r9b(sf5;(c cased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is requiregqn n ;/bgr5r .n+f,v;(f khvnd 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 125(x6ae1kc.yetb0s y d+0-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose,urgnw c0wy*)+rupar7co ur3 hx/),x string exerts an average force of 110 N on the arrow over x7w)rcuayhx,+cuor,3r /g*w)ru 0 np 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 backward 25 cmb:wozk ji )s lzx/7qg59g /m(w when the ball is caught. What was the average force exerted by the bazg/w9o 5sk:/w7mgb)zi j xlq(ll on the glove?    N

If the speed of a car is increased su-t+j*ha k )wby 50%, by what factor will its minimum braking dist t) hkaw*sj+-uance be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measubc8izobr+aat 8( flwj 2pa 13-re a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coeffr8 f1a wab(- 28bpoaljt+zi3cicient 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 m4n(r7oua jbv+y yab.6ass of 0.25 kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the avr7a vn.b(yyjb6o u +a4erage 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 thro kmbdn/u.d:d3m: zjmxo6 38klpn 6yz; lg8f c(wn straight up by someone who does 80.0 J of work on it? Nmkmgbc 363. l:d( nxjkzn86o l /d 8d;p:uymzfeglect air resistance.    m

  A 285-kg load is liftedcc-ur 9.e3;wdan; dk8hnoxp 4caop(/ 22.0 m vertically with an acceleration by a single cable. Determinew 8cun hpanoradc/de. 4-k(3;pxoc 9;
(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 tt8goph ay *, vds p4he86n*6zlfh wx;*his spring be stretched to a* flhe,p*6 ;xodvw6s8pyntg8zh*4h store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher; q fkgdtmdef w0bht7fk3r *79n30 kz1. What is the change in potentigmkdrwn q0te7d tf*0 f;91f3hb z3 7kkal energy?    J

  By how much does the gravitational potential energy of70y*ys5g stah a 64-kg pole vaulter change if his center of mass rises about 4.0 m d5ygs a 0h7y*tsuring the jump?    J

  A 1200-kg car rolling on a horizontal9:d+qn n pnbzlc/:1af surface has 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 za1fqcnb/+9d n :p :lnspring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.20 m abov23crvs(-3hiqbh5o );nzdt zce the ground. What is the potential energy of the ; s3vbot 5hzndi q2-cr(3)hczbook relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and climbs to the top of a 3300-4mxtj fz(2ressnx j t;.6 ,u3om,sux(t2ext 3 oj s;rz64. jmnf peak.
(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 halqzq lr z/5f;(m vgk5to5xqz7rkx35 0 ngs vertically next to a ruler. The end of the spring is next to the 15-cm z3korl7;zl5q0vmt zq/rk gqx 5 fx55( 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 running at top speed (5.3m/s) and grabs 3dpq3a7tm o/ta vine hanging vertically from a o 3tq/dtpm73 atall 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, slide0x c366+ez 1pub1zatmwo -t jjs 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 fr3)wtx0bmo d80 hud*;omgovo 4ictionless 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 kini6q 5w cip s/gjvqkrb51:w)5pr6;gjm etic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her c q5r6 :kvqj1bi6w5 mri/cp; jpg)gw s5enter of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumpsgt+ z)qdkc7v3 s0) njm vertically upward from the top of a platform with a speed of 5.0 mcs)jnm0d)q+gz tk 3v7 /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), wdczs;p-i i3ir e6aef;y:(d ,uhose spring stiffness constant is 950N/m is attached to a table ana yeci6, z( ;r3 iei-dsfup:;dd 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 trackxm5;h uhkj -b6ek, os) shown in Fig. 6–39. If the block is to remain on the track, even at the top of ;uhjxkk6 5m-) ebhs,o 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 sr kler *qeyl3 pv 4k9(c7ho6*qpring (spring stiffness constant k), Fi qe796vq ( 3lherockl4rk*y*pg. 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. lkod 59yyuz3 c,5w a)rShe is tied to a bungee cord whose unstretched length is 12 m, and falls a total u,3d)za9l5 o yky wcr5of 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 dragg;(e6)rjh wb ohed up to point 1 where it is release(h o;6e rhwjb)d from rest. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at an angle mgi)sg+ .+,m1ed t tg6sbz0hg 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 ofz1,x8/obde dh an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g whe hxd/ dbz81oe,n brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up a 7.8 )fhlr hq;08 wui*;wto q8r c)s$^{\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 opposite di/s(tybq 3lr 67kpcl+y rections, /b3sylc( prltk+7q6ycollide head-on 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 rb ; (**cg+6 e9raw7wi9bvs: iojpuassuq*0v 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energse gra 6ua (v*csjr*o *9wib0q7siu9pw:; +v by due to friction was generated in this process?    J

  A ski starts from re.xdj ssv9y2nl so/ +o/b:j3 xbst and slides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is droppk*m4k;u(wry pf6-y jfux.3 cved from a tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bouncer (js4 g8ln9no(r t( p+acp4vds back to a height of 1.5 m.rcsl(9pn a8 jdg rp(+4vo(t4n
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulled across a floo bfh6h-h(+u0e dn4e2rr ytgp2l;qj7 lr with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final+e q6bl(htp 2r;7ng4r hh-j dy2ue0l f speed of the crate?    m/s

  Suppose the roller coaster in Fig. ntv5(75qv.gg am - fqk6–41 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with mkna .gqf(7v5-5q vgt 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 om uvq5f7 fcxxrg9m0- tnqn+* )f a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light horizontal sprx8 k0 jb21jv4lru )ltming (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 stopping and turning back. Whatb2vm8jrl jut x0k41) l is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a h j: i2yzmravvw0j n*u.t/6g+very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of fr0v r2yg iwhuvnj+ /*mtza.j:6 iction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 kg inclufdbs40uo+3j x j(ge2 u(tzn)hding pilot) that was launched horizontally at 500km/h from zt 2ujbh0+j()s(u eod4f3 xn ga 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 sixtpg4kyvt :)h(z r-i2och-story window 16.0 m abo4rti(2z )y -ockpvg:hve?    s

  If a car generates 18 0 yyng1 d0z-)nekfvy7 hp when traveling at a steady 88km/h what must be the average force exerted on tyy1)0eyn0k z -vndf7 ghe car due to friction and air resistance?    N

  A 1400-kg sports car acceleradp .p:lr4ku. btes from rest to 95km/h in 7.4 s. What is the average pow.l:4p.k rd upber delivered by the engine?$\approx$    hp

  (a) Show that one Britishzg)wwa)0 pelk two; vvret* 5 0*fp9y2 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 l21zpv/fkjojy 55hn+ 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 11fd+( eqtz8jd 2 pc(ftn3 (y2yr(9len5gipk(w 50-kg car slows down from to 65km/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 trt e +(8gp2d k39n( lqp(je t( fcwizndy25r(fyaveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in sa to4li*0bu91.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot fr-f f4rp rn7qu5e4wu2 lom rest to 14m/s If this motion takes 1.5 s, what averagelqn ur7pf5f-4ue2w 4r power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of )fdtrv00*vhg)nwpi ;3.60 m. What output rating (watts) should the pgwt0)ird* )nv ;hpfv 0ump motor have?    W

  During a workout, the football players at State U. ran up the stadium ss* dw s*8s+hgstairs in 66 s. The stairs are 140 m long and* gss8wsd+sh* 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 cycln1e5,,nk fi8ke 6m+mjt u o+coist 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 mg*;l; pp blt1qpu8* om)m8 nciaximum power output of 120 hp. How steep a hill can it climb at a8 *mgpq8b* c)p1um plol;int ; constant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to-b.n:m7 sronp2i0o*klq bu t ( drag a 310-kg box along a level floor at a speednm.7n:pi- r(qb *ookt 0 bsl2u of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down7 d60.hdbvazwqm7 o52*wv md p a 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bumpers” tha1lgy t/y/cs6bu-ri2e5xo oi8t 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 test-i1x/ cliues5to /y8 og2yr6b ed by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the ground, and the:u /86qzweef v j:gj*q remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a vf:jw6q uqe8 ge*zj :/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 1) ymihkyjs34 .0x4ds r936 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 at launchy4s d s04 xr3y.ji)hmk if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding withou*nq8e58 axus:co * plut friction along the looped track shown in Fig. 6–39 is to remain on the track at all tim5*s 8uo8c*: aenup lqxes, 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 aftm: p5*mc5sm 0 pdtslnq8t9qo65 *ktgeer jumping from an aircraft without his parachute opening. He landed in a smtt 9t*ds c5p ns6*5e05pgqqmlm8ok:nowbank, 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 7p7 dxg6+oq s(/ (z-mxj upqzzcord of length L whose other end is fixed (Fig. 6–+ 6z7z7jq(x/ gxuq m(zpo-sdp43).
(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 mqiy v3 w/4wj(cgnima u*1a74to the top of a 3700-m-high mountain. The climb is made in 5.0 h stmi/na43 ic*1 v4wwqmy 7a(jugarting at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg ele51e4n5u5 ir d ubbj*itvator 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 7)g s x)afzid4lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the power g7x4 f))zaisdneeded.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vei do)33n(u bkyrtically 81 m before striking the turbine blades. b (33)knd yoiuCalculate
(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.yc +8j b1 3z7fvge i(g)ezvnp6 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 — thv jvn67e3zg1) gibc y+z e8fp(at is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy b/ *0l sq74*;m stmrglbpt:qzfar directly into work, how high could an 82-kg man climb a ladder if he 0:t z4t flbm* /p7qm;qgrl *sswere 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.wzk d;4 fp;+v0iohc: l mkf0p/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 the scale compresses+rvw2/ v5p qvy 0.60 mm, avvqr/+ vwyp 52nd 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?    N

  A 65-kg student runs at 5m/s grabs a ropr,wd 5 *x(ifume, and swings out over a lake (Fig. 6–45). r *wxfim d,5(uHe releases 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(vt 3 uiv7ndr: m in 9.0 s. What minimum power output v 3(7rdvni:u twas used to accomplish this feat?    W

  Some electric-power companies usef/wr b1vm m.yx1:n:zp water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced : : p.z1 m1bvx/nrmyfwin 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 cutawd+(.vh :bl w in half. What is the spring stiffness constant for ea w.wb:alv (dh+ch of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough 3huw+f;7(( *yeb dtle6m m e,gofhcv 7:: qk,xy7 $^{\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 34ef-8l:1rgea:m (upm /; dcqp8us vdk.2 s, how long will it take to accelerate from 5uul: ;ep (c:armsd/m8f1pqk gve 4d8-5km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient walks 5oi.nc d hd;;oon an io.; hiddoc n5;nclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a distanceu9b9dpyi i6s5w pog00 ti*k;q of 500 m, what was iibw0q9*;pd ytpk60oi9i s gu5ts 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 fr,w;xxi2o :a 0wzp1 mmrom a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is its maximum poweamwim;,owxz0 1px r2: r output?    W
(b) What is the speed of the water as it hits the wheel?    m/s