In what ways is the word “work” as used in everyday language the same as6ad0hdrzg9k1h7 k+d x that defined in physics? In what way7k6r+xa k9 zddgd 1hh0s is it different? Give examples of both.

Can a centripetal force ever do x.a.+ ipdjj6mz84t o cwork on an object? Explain.

Can the normal force on an object ever do wodis)r2 zmvjr j 4;5p8rrk? Explain.

A woman swimming upstream is not moving with respect to the p1/wuvnvr :s0shore. Is she doing any work? If she stops sw w/s: nuvp1vr0imming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negativeb80wyn2/z5 4mcsx ue vn.- tvd? [Hint: Consider what happens to the dishes when you pull a tablecloth ouc/42n v-b5t8z.dswv0nyxemu t from under them.]

Why is it tiring to push hard against a solid wall even though you w,f;fn yu24 ior)l7jx+;uul1 gayup, are doing no winr jx ; oy + ;ap)7uy21lgfu4ufw,l,uork?

You have two springs that are ident,qk bnp6ka8m;ical except that spring l is stiffer than spring 2apm,;86k nq kb $(k_1>k_2).$ 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 pn mltvi4kzx .wl*o5r)0:a a- that is free to slide on a frictionless skiw-zr.n40:a v pxom) 5a *tllurface (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitab:,qbor : 8ceational potential energy change when you jump as high as y:,ab :c rboeq8ou can?

In Fig. 6–31, water ballc 0svl8 -crpi;oons are tossed from the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed8ci0 lpsr c;v- on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest poiva,; ki2)nv5g+hj/iw xaa(p xnt 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 a haaxgj,vp;5k2i+a vi)n/w x( long 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 uprigh*qh o97k j8wld7na2jht on a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the lahadj *72q lwo8hk j97nw of conservation of energy.

A bowling ball is hung fr fq ,c4xkb1+3fc.45myuc y /g oppx4nlom the ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release theblm up,k4+ qg4pxx1fc 53c/ofc y. ny4 ball without pushing it. Why?

What happens to the gravitational potential energy when water at the top of ahk4rc9 ep6g,ba1hu5 u watcug4he9r p5,bh6aku 1erfall falls to the pool below?

Describe the energy transformations i 1fb5jihftfr 4ho:2. when a child hops around on a pogo stick.

Describe the energy transformations that take place when a skier startswkg ur .i.gc k8-vgov7 t:n97e skiing down a hill, but after a time is brought to rest by striking a snowdrigwnv rcei7v - gkuk7:gt.o 8.9ft.

A child on a sled (total mass m) starts from rest e)h:t 4b hm 6*34p8 va agnf.mljk:zsiat the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and f z: s8tmh.vm6h4*b 3 npi4 ej)k:laagthere is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rather than stepph5u6p ,/cijyc(m6is ji /j5 u(ihy, cpmcijs66ng on top and jumping down on the other side. Explain.

Two identical arrows, one with twice the speed h1tweac3sr( s /hw m-:of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the crh /hw(m e st:s-w31afaster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion ofp (t xr+ia3pg- a simple swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clgt ( aix-rp+3pock has to be wound up.

When a “superball” is dropped, can it rebound ah80nme/y8p4yc jd8e to a height greater than its original height? Ex/n4 8dm ya8ephye08cj plain.

Suppose you lift a suitcase from the floor to a table. The work you do on tht v,ca 1eb9:.cb,hvx we suitcase depends cewthbcx9 1,:bv.va , on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for-/womb )/nrynfbpl9 * the power needed rather than the work.

Why is it easier to climb a mofme ,n:lh kmrro2(0j:;xgf n8untain via a zigzag trail than to climb straight upkg0, fl;j:2x fenrm( :omhr 8n?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropesj1 ysk;i tg82k to decrease the force needed to rai8gt 1i;kksy2 jse a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitationa (1n+ .;ly+tpntf fluul force when a 265-kg pile driver falls 2tnt+1f.ypu ul(l;f+ n.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work .cjt 1yc,zpd/f5bx ; tis requ5dyc/, t. fxztj1b;cpired?    J

  A 1300-N crate rests on the floor. Howfi22thq7g ci4 much work is required to move it at constant speed (a) 4.0 m aloni4 ghc i7qt2f2g 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 crateb/fs4gm g:ctgy+78hv 10.3 m acro8hb ggcs+g/v fty:7m4ss a rough floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a fr/-0f b4q0pq tn5cinploor at a rate of for 7.0 s. bp 0c-5nir4 f0nqptq /Find the net work done on the box.   J

  Eight books, each 4.3 cosc:xk t p:+) 9bc-rmrm thick with mass 1.7 kg, lie flat on a table. How much work is rer:t c+ os9m):brxk -cpquired to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 c6 ikbmz.wvq772b6vvi an be used to liff objects we might not otherwise be able to liff. Show that the rivw2i6mvqbvb77 6.k zatio 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 a6/diox5;qf ,601upoio:+yober1ta,khx im and is kept from accelerating by a man who is pumor;,e/kh aa ,iyx0 1 5d qif+oxu1oop 6i6t:bshing 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 helicopte -xcj*to6 -es qv)sl)er of mass M an acceleration of 0.10 g upward.lx-te jqevc-) os* s)6    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 disaisml:6cj; 4te6u)i utance 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 object9wmy bsm9x4qi, ym;1c4 3i xpgj2b :hn, acting along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m to x = 10 m gm ys:4i9m3xcnbm1ji4x;2y , q9bhwp    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 pas( 8c y,orw(c-6 y 7au/ xd36ztaltnvzrticle acts 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;bd7e sdbud 6) mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor has its sp5 1pj;lv swej .jk6cv3eed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required +n.,n jwm6/wkjehyx1 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- s78jzx1 ,2ia-mxswnrkgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an ave-v w(ypzj;,2s 0s hmhs8syt+qrage force of 110 N on the arrow over a distance of 78 cm. What is the speed of the ars0-;2 8wmzsyjsh vtyq(+psh,row as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward liz * 5gsz()wpwve lv a;ju00.25 cm when the ball is caught. What was the average )zeipul .lw*5az0 gv(w0; vsjforce exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by whmh l7 edf w-f-ji8-z/fat factor will its minimum braking distance be increased, assuming all else is the same? Ignore thhji -w7md -fz f8-el/fe driver’s reaction time.

  At an accident scene on a level roawnf9bb ul ia2o kgn-:05t2ad8d, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the af2n :d2angtw kb9i b0l-o5 8ucoefficient 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 of 0.25 kg is pitched at By the time it reab cjk h.91eljp(u *;*h7d, xk8uvllrwches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance upv** ,h lbj klrh(djx;.187lec9 kuwduring 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 straigmh(:jys99 b(d+scuwr ht up by someone who does 80.0 J of wh mu w9j+r(sbdy9cs(: ork on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0i o691cth6 jle m vertically with an acceleration by a single cabl1hocj 9liet 66e. Determine
(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 con)r+2nsgy, -x6erdevy stant, k, of 440N/m How much must this spring be stretched to store 25 J of potentialy)der2n-v +, 6 xgsrey energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. Whai1ryp4 fuhapn 9v t.98+lnul.lqu4 7yt is the change in potential energy.q4n+ u9vl8ll.yyf p7 tiprhn4 9a1 uu?    J

  By how much does the gravitationalkn 4mn4g pksv:k/a4 pmpwz;. 1 potential energy of a 64-kg pole vaulter change i ;4km 1vpp4:mgapz4 kknwsn./ f his center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h when itn7 vemja twlgk p8hmg)* +)b 7os53-yg strikes a horizontal coiled spring kpmt3og*j yb )h7-gvn8mlw5+7sega)and is brought to rest 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 tjqi 5 3seqo y*mew,,+xn) klu2 pn;2fthe ground so it is 2.20 m above the ground. What is the potentia5,i j uqlnwf*;ypqm,oxtkee22s +)3 nl energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation 8 cj dci9ck:-yf07ma uof 1600 m and climbs to the top of a 3300-m peakyc8f7 -kcm0jiu9c da :.
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically next to a /*ldb1isn ig 7j a1-jtruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg ma1 sitjglnjbi*- da1/7 ss 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,+ d5l31pcnp44 ieywun is running at top speed (5.3m/s) and grabs a vine hanging vertically from a ta +5 4wpniy1p4nle 3dcull tree in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frictionless 35.0y jrj(-atv9g+5j,fda)hr c7 x$^{\circ}$ 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 *faxr*bcb 3,a shove up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic enh0eue 2ue2c0k5 .iy:z wll5v nergy 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 center of mass 2.10 m and cross the bar with a speed of 0.7k0il :uhlc e v5ze.w202ne5yum/s.    m/s

  A 65-kg trampoline artist jumps verticalp-s:5cec4 lz yly upward from the top of a platform with a sp4ecy-cz: 5ps leed 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 95047 d.crb gbbh(N/m is attached to a table and is compressed down 0.150 m. (a) 7hr (b .b4dcbgWhat 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 shown iiqy q n1qxl:p,2hprm-j6 8o aw4kv+r2n Fig. 6–39. If the block is to remain on the+l-qqiwx12m8y6,p:jahp q4n ro rvk2 track, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spriabjd grkw) 7ry/(o6z,ng (spring stiffness constant k)awydk, b 7 )r/6(ogrzj, 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 bun uy ao8 ,*wlfdh0zkon1l .:)zegee cord 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 law appliz)en0 fy.d: 1*lak,olhw8uzoes. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6t-umd5 eykqd 3r.. 2ag–41 is dragged up to point 1 where it is released from rest. Assumin-.mrt.yd gd2 kqu 5e3ag 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 of 339tc4cn n7 mjo7q/rzp : $^{\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 thesl p4 +v *+kwjkb:ba x-x1k,j1 lpol7m bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should llj*1s+1 mkxxl+bjp kbvak p7w4o-: ,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)f+x/gjr-njd tizszo10.r 9 b 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 ub7oy71yr,m akg and traveling 95km/h in opposite directions, collide head-on and come to rest.7by 1o 7,ayrmu 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 reaches the bottom wu4vxh 57hg8-. fukw/ md k29nbzw; wshith a speed of 2. z4 h7w sv-b5xhn fkg.2mh9dww;k/u8u2m/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from restny vb 5p3jz4 ii( fu/z;-udy(e 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 dropped x+6ki2ya :bwt 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, ana o5 n7q6 irfg7whn.8td it bounces back to a height of 1.5 mt n7rf5a8io.6h w7qgn.
(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 re*nbj) zns90wk st, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for t b0)*z9 nwsnkjhe 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 poix)5*dqm zs fbj,n nnr2l8a6 o6nt 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will rmz qn*bn)6fjs 6d8 o 5xal,n2it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady upwardbfk05;,2:sinepx nmy1h z w5t 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 k7va da7* 0jy/mv dt/mto a very light 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 be0 ykajmma v d7d7vt*//yond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal spring, F2g vycv (qcfc 9fd21bql*-.eaig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A(df2gfc9 bv va .c2yclqe1q* - 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 spa1)4bnb/-xa 4h5 )uzlasmpcq i ce shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3zapi nacx5mus )4/lqbbh-) 14500 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 175bm kuwdid)hk4p3nlc2 .l: curk70k50 0-W motor to lift a 315-kg piano to a sixth-story window 16.0 .0d7pwh4b 5k i0:3kr kcudllc)ukn2m m above?    s

  If a car generates 18 hp when traveling at a steady 88km/5yju52xqt ifg6:c23l al5jibh what must be the average force bj2u 6 3ctl55xj ygi2l iqfa5:exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates y (iz ynhg;ya0 (pti/)0ak7fafrom rest to 95km/h in 7.4 s. What is the average power delivered by the enginy;700pa/fiakzi hnay()t (gy e?$\approx$    hp

  (a) Show that one British 0mrb2 wi(.ryx ntw2c (v(x:sz horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed ixrpb5 )k2vvz4f6 7owa n 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 slps(2ulh i 12b jm/-wgfows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (wfli(g2 phum2 bw s/1-jatts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1.0 bsfkr2kh 5d+8u3 +taj h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s pdwfqp- zc)3n8bvwt. ; x21gr wh 3vj6If this motion takes 1.5 s, what average power was tgb)p w hcqwwr1p3;.vn x3f-jvz 682ddeveloped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m. Wvfap ;e)7l q 2a2 +rr1/ulyrbahat output rating (watts) should a/1raveary q7+2 b;r u2)lpflthe pump motor have?    W

  During a workout, the football players at State U. ran up the stadium stav-jyjtv (: 9k1wewt5b irs in 66 s. The staiy1-j:t e wjtb(5wkv9vrs 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 zs(zayt.cpee 4f3oq x u)7-0i6.0 $^{\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 a hii2,w4)snrtov0 n ai4y:bt 5mgr66r r all can it climb at a constant speed of 75km/h if the frictional forces add )vb tm nrw r26 440ar sioni5gtrya6,:up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be ablncms-gd 40 ,vde to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of friction sdn4 d gv0mc,-is 0.45?    hp

  A bicyclist coasts do;qoh8 +fa 2fh4yaf0 hlwn 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(8k)fog-/u0 o)n xbigh 2vm/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 aovf2g-b)hg)/ox0n u i 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:8va))lbhkzm pym3i; -f xfy3 t 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 shelf holds 25 books, how m:k-m3yfz mvx bp8l3 hy)i f;a)uch 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 r/o oha)w* (ccqao-*l 1936 Olympics shows that h)/*c oq wcrolo-(h*aa is 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 he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding witho,qvroi(n6wbr )n0ze9ut friction along the looped track shown in Fig. 6–39 is to w6o qe (9i,nrn) zrb0vremain 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 wpjpmvmxnrxeg;,,: o3l t 368 aithout his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Ass mx,tg6a ,8j e3v;olpmpn:x3ruming 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 hoc2*c :0 ( 3x.x3npb*v clxpga sq)bqcvrizontal cord of length L whose other end is fixed (Fig.*blc)vx* 0 gxsx c(v cnq33:2.pcpaqb 6–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountaiz6 ,ak*3tx-gr uqw,rwn. The climb is made in 5.0 h starting at an elevation of 2300 m3-6qw*t a,wrur, zgxk. 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 m abon1h,t(pw3-19dze jhi :pc nktve 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 it xpyb/f4 fi50ts lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically 4fi/ xtbpf05y) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 65m1cg)qb91+us ,bqowq(d e :kc 0kg/s and falls vertically 81 m before striking the turbine blades. Calcul9 keq qc ubs:bgd11,w+o)q m(cate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (Fig. 6–44h(t37m5h qb7egse4vt), 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 your speed is above the minimum needed, this anse7t75q( 3gh hebvt 4mswer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body cou,5 ;dscbny+p+c-ze x5nu n e.gld convert a candy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=1000knx+bu-p cd nc5;,s+n .eze 5gyJ)    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 zs3 5xrw:ibtu qiu /-2of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the syd 2k1,8 fk9ghnxcqzdl4uv: 3 cale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a heil1fxcgny:4hu283vk,q k zdd9 ght of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over7i:tb- xsk2okqg 91 qz a lake (Fig. 6–45). He releases the rope when h sokzi7x2k9q1q t- g:bis 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 vertiv) e7wr(y u,pmcal distance of 5.0 m in 9.0 s. What minimum power output was used to ) ,uvr( yme7pwaccomplish this feat?    W

  Some electric-power compann5b+klzb;xq mucr1 h96xi 73 vies use water to store energy. Water is pumped by reversible turbine pumps frnubzx76xc35+iv1h;b mrq k 9lom 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 the sprinpq (,i6f3s nycg stiffness constant for each of the two ryp i36(qf,scn esulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough 37jzet-;m rs/ 0t $^{\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 3.2 s, how s o2+ntr x u0t-+ial,2ljty5j long will it taol ,2rtajl0jy 5 ++-ixt s2nutke to accelerate from 55km/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”), t ce-orosg d8(s8r +;wwhe patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is slopinsor; rwc-(w ds+8g8 eog 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 f fjy47o1 f/bgn owq7y2:g3ee distance of 500 m, what was its velocity when it left the volcano? jef7oy3/ woyef q2ng4 fb g:17$\approx$    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 radi*v u0l0+7q2dbmupz te of 95kg/s (a) If this water wheel is set up to provide electricity output, what is its maximupldm2 u *00d uq7vzib+m power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s