In what ways is the word “work” as used s 7x0y af fzm;jpycu:,tq5hc) .jfz,3in everyday language the same as that defined in physics? In what ways is 05 m .7u hyj,c:) yjxfptc zs;q,zaff3it different? Give examples of both.

Can a centripetal force ever do work on an object? Explaimj(-w (s feed ygat33+n.

Can the normal force on an object ever d /a/m)d ja kjjk6u t(jqu-mv1*o work? Explain.

A woman swimming upstream is not moving with respect to th kx.ib/ f 61jqkkqwg94e shore. Is she doing any work? If she stops s kbqj1f 9kxqw/i64.gkwimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: * qiuo2mi6)9 ifcv4ri Consider what happens to the dishes when you pull a tablecli vqiirf)46cim2ou*9 oth out from under them.]

Why is it tiring to push hard against a solid wall even though you are doin7 i7(d6umve v;0eylj (0knbz vg no work0v7ev ;7b(d i0mk(elzuny6v j?

You have two springs that j+ anadwr-)1 6davyq6 are identical except that spring l is stiffer than spring-daa jrd vn6w)+1 ya6q 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 frq 0dj/;vf 8uxuee to slide on a frictionless surface (Fig.6-30). Thefjx 0uuv 8qd/; block starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potent+wh2w7 4n jiltial energy change when you jump as high as yoj+nil wwt247hu can?

In Fig. 6–31, water balloons are tossed from the roof of a b.+. h sz,kjdzquilding, all with the same speed but with different launch angles. Which one has the highest speed on impacjzk hsz+.d q,.t? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest point in.y xba ,3hzwossxggn,9) 6:us 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 directedu93,xx6w,. gs)gy:s b znsoah 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 onm ufhr9* 8zy;c a table. If you compress the spring by pressing down with youh8r*fz;9 ymcu r 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). The instrsi9hu1ncen )(uctor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is 9ien ( chns)1usupposed to release the ball without pushing it. Why?

What happens to the graviba(cnx k30s0 lxeh; 9ttational potential energy when water at the top of a waterfall falls to the po;tn3xc (l09ba 0 hksexol below?

Describe the energy transformations when a child hops around on a pogo ie/ +by+ts-mpt f3an*stick.

Describe the energy transformations that take place when a skier starts skiingd2:z.lb()y mjb 1yw) va w uj:iahb;l. down am (: j;l2w.vibdw 1h:ab .)lbzy) uajy hill, but after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the;kfeg(5.rp l ) ehm*iz 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 there is no friction, an.e;5z gp)(il femrhk *d (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in theiwasc2)u:t 1pt )qj y5tr path rather than stepps 52 wttuy) )ca:jptq1ing on top and jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the,r3+ v)ake 6fu k nugr2zjz/o5 other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than th/kvra2z g,3rkjf6) nu oe5uz+e slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy, gn x.7v:e+ha2fah* dcc eud v. 98vi2a(a) ignoring friction, and (b) taking friction into account. Explain why .ca x*u:v.a d+7aihvn98 e2ghev d2 cfa grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a heighpma4 8 57dajg9p(rtqpt greater than its original heppd g 85amqj4r 7ap9t(ight? Explain.

Suppose you lift a suitcase from the floor to a table. The work you do on t4 ia*z h6)l4xwl fo-nrhe suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the heh44la fl*ix)zr6 own-ight of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than the wm6b 9w7czjabwux/ s-:ork.

Why is it easier to climb a mountain via a zigzag trail than to 9e6twvahp+ l, climb straight up?wp ta9,l 6hv+e

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes to vmn7 mj(j*p4iiz n,e0decrease the force needed t z,i7pm*ij(4 e0nv jmno raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pile driver fall71hdaxe4t q/i hl1ola( u.s (ys 1(la 7 adh .xi(u 1tlesyh4oq/2.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work is re+7vl txk ,2rx nda3 k7vi 7pes94h0k6o5b czcgquir0aved vh73zkic576 p2x4t9cs k+, k gbroxl7ned?    J

  A 1300-N crate rests on the floor. How much work is required to mo(ykxk9ien+ ;vh ,bno4o gqv)-ve it at constant speed (a) 4.0 m along the floor against a friction force of 230 N,k( qgooi -+bnx9e4nkv;) y,h v    J
(b) 4.0 m vertically?    J

  (I) How much work dij 6 ;z,4ybdsdo4*m+t gcvqq+e d the movers do (horizontally) pushing a 160-kg crate 10.3 m across a s qe++4 yc4 vmodq j6;zgd*,tbrough floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a forc63 j0nwo e0jzze across a floor at a rate of for 7.0 s. Find the netz006wjn j zeo3 work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie f x;0l5c+ gzk.k6 yrjculat on a table. How much work is required to stack them one on top of angx5jrclc6ku y ;.kz+ 0other?    J

A lever such as that shown in Fig. 6-35 can be use-ki .h1pb2la emreo vap( 7-t7d to liff objects we might not otherwise -7e.bip2ae tmoa pk-(r7l1v h 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 kepbk5- r;vanqey/z6)cb t from accelerating by a man who is pushing back on it parallel to the incline (Fig. qynzv5-/rk ce)6abb ; 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 t x3lu fvtwoq2* vc+,8bo give a helicopter of mass M an acceleration of 0.10 g* vctv wf,qb+3x82oul 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 v6uoj6,9r.bpn(0x+ ze ivx hm*w5jocp w (s2vdistance axis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varie1gd3+f4 hccui1ztg( zs as shown in Fig. 6–37. Determine the work done by this1uci4g th z(+g1 3dzcf 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 ad/ebde/149 nfohl 2xv cts 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 mfo58jq fj8vec 0fl)n9ass 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 speedjhl;bf4qf - -x increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is requxct,z95mq- j5cj i t3rired 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 m.qoq+u-*cojn)nnon2hi :-k done to stop a 1250-kgcar 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 average force of 110 N 7 nx+miokc+7ypq-bu 1 kd*gv 9on the arrow over a distance of 78 cm. What is the speed of the arrow co 7xkg k+*97yvpq +1dnb-imu as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25 po7*ba1(1xvuk xsz0u cm when the ball is caught. What was the average force exerted vu k1 zo 1x(ausb7xp*0by the ball on the glove?    N

If the speed of a cari5pa b4/la,s w is increased by 50%, by what factor will its minimum braking distance be increa p/5 sw4lai,absed, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s skid mark /kyffp4t/ g+70 es1b y io/u*f2 mglwbto be 88 m long. The accident occurred on a rainfyg//i2 4o+/0 utlsygfb1 *ekpbmf 7w y 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 of 0.25 kg is pitched at v.1+*aeofglr*ulqzt6- u1o+ b zb 7je By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the p eub z*tv+jle lo+6o.fr1 b-z 1a7qug*itcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone whr+y,ek0xpgf65e-s g ro does 80.0 J x5y6 re k0fs-+pr,ggeof work on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a sinqi5nr s+,dpd) gle cable. Ddq d)si,rpn5+ etermine
(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 mg -*5gj4v.mmqnd bie)uch must this spring be stretched to store 25 J of potential enerj em-gn i g45qbdv.m)*gy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is thv8,v.hbp2vh d7 ng; ;uy ve.p,ao0euwe change in potvypu 8;gov.0h.; wh v,e,27ndue p bavential energy?    J

  By how much does the gravitational potential energyr(yf mnuzaqx1(z0 2v9 of a 64-kg pole vaulter change if hisyruvxzq(9(2n a0mf1z center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling onby3ny1/ b,l 6qzit 4bv a horizontal 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. 46/vn3l zbtiby1qy b,What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.2 gg o/07g9vuan0 m above th noggg90/uv7ae ground. What is the potential energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and cl3:wjsc 7l zs4zimbs to the top of a 3300-m3cz4:7ls w jzs 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 3;tuo j( ik3jw:lamqwkc -i++hangs vertically next to a ruler. The end of the spring oc uw3(+ kiimt :ljwa;+-kqj3 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 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) al vv5z( a;f.amnd grabs a vine hanging vertically from a tall tree in the jungle. av(a5f.z ; vlmHow high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rf1ml w+qn a(bd4s8i 4cest, 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 frictionless 28.0xmyr2cl) 2kz 3)v )fgw$^{\circ}$ 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’sto( -* bgzsoj+fe 1i6(sahni 5 kinetic energy is transformed into gravitational potential energy without the 6*nisog a+bjfei(zo1t(sh5-aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward frotw 8-.ti. tvczm the top of a platform with a speed of 5.0 8zwv -itc .t.tm/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 95dkz 7:pig 2fr+ye d/g-0N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to + zi: dekg7/g2 yf-drpa 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 frictdzmmm( z t35);qdlbnn*m t0 3fion along the looped track shown in Fig. 6–39. If the block is to remain on the track, even m tmmm5nldz ;0d3 t*3)bznq(fat the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring sti+2y v x(damh:.fic 2kfffness constant k), Fig. 6–40. The block is given an initial displacemenci k:f 2+2ma(d hf.yxvt $x_0$ 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 * rzrsvh0:8tvtied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculat:sthr*8 vv r0ze 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 draggeduwph,)h 5b,uy .y9 ,ruuozmun*da,1 f up to point 1 where it is released from rest. Assuming zh.1p yu auuom*,,y)b,5ufrn9wud h,no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is th1:dvs+ yg , kjlsqf(zacm 4+4irown with a speed of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottom of an ip-guhi 4b3 feas4(a+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 shouls(ii4pb-3 +e4u haag fd 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 up a 7.n0ji;)y jd9 q: x- ic8ks:qnuy8 $^{\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/h7 97hw ,jouxcm*ko *ka in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this collisixmkou 7 *7h,oc*9w jakon? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high amie 16e;0s c( jn ;atzv6nkr3+xx9fcend reaches the bottom with a speed of 2.2m/s How much thermal enjs3fxez6c6m(kix0 n n;;ae 91vrc t+eergy due to friction was generated in this process?    J

  A ski starts from rest0*vnw r :ms69j 9lrhmpka41ie 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 from a tree 13.0 m above the grn ok ato*8s(w/ound.
(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 :.vby ) (q*nhtps ,92ikjrizkm, and it bounces back to a height of 1.5 m)bip*nk (j2vyskh,r .zi 9tq:.
(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, starcjm:t6s pi. ;) c4tsbbting from rest, is pulled across a floor with a constant horizontal force of 350 N. 6msp :sb4; jibtt. c)cFor 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 speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed alqfzhvd 43;2d.lw1b of If the average force of friction is equal to l fa v3;b12d.lwdqhz4 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/ot 6; jz3th.cwl3q6g rs reaches the foot of 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 a8ufp.l waww r.14hk 3m)4 ccmo 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 beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friw 48uhcpl) 4mf1 owca..w3 krmction between the block and the table?   

  A 280-g wood block is firmly attached to 0,- zr-ba- an s4ulx n377vjgj/ b-0txgqybsxa 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 t-gjy s -b4xvx0-7b073nr,zgsbq-j luan a/x 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 “glhuwm ,xr5 ; m fv1a66ru3a,lmaider” (mass of 980 kg including pilot) that was launched horizontlmmx rrav15f au366a ;,,whmually 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-storg p r)udr05)lfn44kpry window 16.0 m above)pr 0d 5p4nr)grflk 4u?    s

  If a car generates 18 hp when traveling at a steady 88km/h whap( x9a5 kpqlu;t must be the average force exerted on 9xl;5 kpua(p qthe car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 79)do9d(9das39g i7kpm q cko x.4 s. What is the average pod9s o)x79 kqg9dik3dcmopa 9 (wer delivered by the engine?$\approx$    hp

  (a) Show that one British horsepoweru+vuff8jkb a(j-zs 2 ;zef /i.$ \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 expreky83yn .v0dis5 2iuvk ssed 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 down from to 65km/h in about 6.0 hgyyy2u( )o me 775 w(c/rm:sv 6xge-+ ilgrexs on r72lyg5xog)( c+ym:g6-u sh(m v7ey/ eweirx the level when it is in 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 motor do in 1osn5a *2jx h,(r0 aedt.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from reslbp +h3vo3 ww:t to 14m/s If this motion takes 1.5 s,vb3w:wh pl o+3 what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of- e0-/o:w7xnavpnw ait0a5s z water per minute through a height of 3.60 m. What output rpzn-sixna- 7w wav :50 eta/o0ating (watts) should the pump motor have?    W

  During a workout, the football players at State U. ran up the stadi;egm x.azc +sl x7;h(qum stairs in 66 s. The stairs are 140 m long .x;q7zhe (;+csgxmaland inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb a 6.0ynhmyri 7cg7 q9 5pvcnk;f 1-, $^{\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 ste(xr 2z.) uojyzs cx649 p.8mer:wfd31b hxz hlep a hill can it climb at a cpmox214u .h3hewyfrlj .) r:sx zzc dz9b6(x8onstant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower musswgcljee16 ,u, 6gj)mt 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 ceg61 sugw j6cl)e, ,mjoefficient of friction is 0.45?    hp

  A bicyclist coasts down a er,b8i n+c(5f ovat2a 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” tz*dn:lyqy b ;3 uu8la.hat are designed to compress and rebound elastically without any physical damage at speeds below 8km/h*.a3d 8 :yln;z yblquu If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first sf ok t;.kpr1.h: dwb,bhelf 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 much work is required to fill all the shelves, assumw.trb. p,f1hodb; kk:ing 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 Olq)- um26xka ykvv 2i3jympics 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 he was traveling at 6.53v 2u62) iyj m-avqkxkm/s at the top of the arc?   m/s

  The block of mass m sliding without friction aledgtl3 4xfr2nmf:r 1 -l+0zzrong the looped track shown in Fig. 6–39 is to remain o+l: m2lfdr3rz1 4-r 0 fzegntxn 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 h0mng uc7 ;5nz n6b+oo53h amp370 m after jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilap 7h n uzm +hnbog56;53cnom0ot’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 tocew xr) 37hf7p a horizontal cord of length L whose other end is fixed (Fig. 6–xcfh3e77w )r p43).
(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 climbc59iwcq o /f8w y7 oehkr(u7,a is made in 5.0 h starting at an elevation of 2300 m. C9k,hr8u/c wyecqo7wo(5a7f ialculate
(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 d- r75bepjnv4uf3 w+na 920-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can move 47,000 u dq/+t fy:dtcd:tt:) people per hour. If the average lift carries people about 2qt:t)dt: y+ /t:fcudd 00 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s anigf,d b5 1kyo.cg1oi3 d falls vertically 81 m before striking the turbine bladeg i db3.o5cgfo1y,1iks. 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 with a circulya6*o9e / mfguar vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of f6*oy/ uae mg9the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar d ,5s f1ump+essirectly into work, how high could an 82-5sfme + ,spu1skg 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 of0 ga/ia5/x vpq 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 insiktft p36o -n731 gozsnmd:su6l:app 1de the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a hzs3 6pml1 ong3f:do tks6nup-7p:a1teight of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs atld7anllzk -9.v b g*:t 5m/s grabs a rope, and swings out over a lake (Fig. 6–45). He releases the rald.l l zbn-* 97vk:gtope 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 w8*x a p.ohq0tm in 9.0 s. What minimum power output was used to accomplish this o8wth .*q0ax pfeat?    W

  Some electric-power companies use water to store energy,dk m3ilh.9* /ppdju5p ogu:c . Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the ener/c 9:di3 uoup.pgmhl5p ,jdk* gy 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 they2 wtc ttfg.hpx(5 w;c+g1 t2*ul7qev spring stiffness constant for ew2qg* 2g7tvw.cyctpth +1 u5tfe(;l x ach of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough rq :yx 2piljp7;p mk8kuf :83t37 $^{\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 accelera6q 3z+nsxu.rgzy ny nud2nvaq(u : ,adk3)s32 te from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same u6 qz unks3d3dgaaysxnuq(,yz2v +nn :3r.2 ), and neglect frictional losses.    s

  In a common test for capnky1ta a *sxoa(6s8usau -0c 87bt7zrdiac function (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is zcub-108 7y tasatu x6skan*7s8a (opsloping 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 upwarjdcocq8a) ,jfk 2q7c0d a distance of 500 m, what was its velocity w 8o0d 2qkj7aqc f)cj,chen it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a rate of 95bb; ,nayzq qelcb55 78kg/s (a) If this water wheel is set up to provide electricity outpuqq ; y,bl8c n5azb5eb7t, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s