In what ways is the word “work” as used ge+e *m8m 7smlevp8/iu8qu 7voh 21 pfin everyday language the same as that defined/7vi 888qgphu vef 2pm7+om*l1 u eesm in physics? In what ways is it different? Give examples of both.

Can a centripetal force ever do work o,/.h5wxp lsf dt,r u9dn an object? Explain.

Can the normal force on an object ever do work? Exwczk,:j3:(adr *sij.ioc n 6zplain.

A woman swimming upstream is not movc01v;c jjz;wp ing with respect to the shore. Is she doing any work? If ;w;zjj0 1pccvshe stops swimming and merely floats, is work done on her?

Is the work done by kineg pb3 dnvwst. 7:e7swqd,vvm *xcy9) :tic friction forces always negative? [Hint: Consider what happens to the dishes when youvw:xytw.c 9 s,7gvme3dbns:)q v7d* p pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid pajtx5 l6v6u/l dv6 .rwall even though you are doing no wovu6/.llj 6dr6taxp 5vrk?

You have two springs that are identibz-vp eqyx; )0cal except that spring l is stiffer than spring 2pex -vq)z0 ;yb $(k_1>k_2).$ 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 tha 9e0-wpmwxyg0jf h9l+t is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, anxm 9yw+g- e0h j9fplw0d 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 gr5gzlj9jru-bx5 l ;*9. s9psnu g ,sxnoavitational potential energy change when you jump as high as you cagn5prjbgzso.5j9 l,x*9 nl 9usu;-sxn?

In Fig. 6–31, water ballotd0 yzn ,qewfp9:aa38yn gr5ihz* :;uons are tossed from the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on uyeh8rt: p3zqa:f,n*5z0y d9iw a gn; impact? Ignore air resistance.

A pendulum is launched from a point that is a height h anxk /ew p 4 8ddh5-d2-t ;1ih2ykikfclbove its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given -kthilk1e x2f8di pd/n yk2 d4w5;- hcan 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 compress3 -f;upi7a zy/bwiuk5 the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the fb iiw y;u 3p7-5/uzaklaw of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6ta rhcu .v;rg5u9g8c (–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor isuu. rrg cth8vg c59a;( supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when water at the top of a w aa3.gv 0,oqwnmj 7s.0spoas 6aterfall falls to the pool belo 3sa .07s ga,6v.0wj noasqompw?

Describe the energy transformations wheae 0fwr-zhhzn-6(x .nn a child hops around on a pogo stick.

Describe the energy transformations that take m2h av0*p gxx md;9d1bplace when a skier starts skiing down a hill, but after a dh g90md;x max 2v*p1btime is brought to rest by striking a snowdrift.

A child on a sled (total mass mpiexo(hmd zz51s ql ,* t2505t .jonkh) starts from rest at 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 there is no frict s,n1q.hedo mk5t*i5lzojpx 20 thz5(ion, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step o/:glc2iw9t; ,qqp ixu(hzd1 mver a fallen log in their path rather than stepping on top and jumping down on 2zg/qm hd( 9piuc,t1l ;iq:wx the other side. Explain.

Two identical arrows, one with twice the spedmy7uhir d t//rlmc49 8ssp ,2ed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the 74yc sutr mrd/h m/, s829lpdifaster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum ine oc8y fq).z(f terms of energy, (a) ignoring friction, and (b) taking frictio .cy fzf(qoe8)n into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater bmgr tts8qua03dc6 67 than its original height? Explaint 60dqbac 37ts6g8rum .

Suppose you lift a suitcase from the floor to a table. The work you do dhjwei9pi1w s)u g12v:p )6bhon the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the si d bhi)1w91):u6p pvg2ewh jtable, and (d) the weight of the suitcase?

Repeat Question 22 for the power needcr:he- 3ye 4gvw)fy:z7e j v2sed rather than the work.

Why is it easier to climb a mountain via a39l*dh4 sybuv zigzag trail than to climb straight up?vl9 4y3udh*s b

Recall from Chapter 4, Example 4–14, th7 4 ;9kc1cmevepokf tq8w59evat you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for ef;185eccoqpkv wm79e9k 4ve t very 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 gravitapwm95g . ue0rrtional force when a 265-kg pile driver falls 2.80 m? uem rw.pr9 0g5   J

  A 65.0-kg firefighter climbs a flight of st;df q ym1v)d3kairs 20.0 m high. How much work is required? d;13vqkf y)d m   J

  A 1300-N crate rests on the floor. How much work is required to move it at 2h- vq qkpq)wl0 (yad1constant speed (a) 4.0 m alow2da )kq0pyqq1l(-h vng 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 crate3tfyx:u94taz(9t nh( kzt 3v8+ohtvu 10.3 m acr 9x:f v3kzahtvo83+(utut9zt 4nht( y oss 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 floor at a rate of 7/:xg1 whk uhlfor 7.0 s. Find the net work done on the b17 hxkulwh/g:ox.   J

  Eight books, each 4.3 cm thick with mass 1 ;, k+u-es ufy8:wjpjt.7 kg, lie flat on a table. How much work is required to stack them :k-ft j8s;ewjy+up,u one on top of another?    J

A lever such as that shown in Fin yow1bl 5o5 oei:+,z,any(uvg. 6-35 can be used to liff objects we might not otherwise be able to liff. Show that the ratio of outpuv,ly uoyaez55nob(iwo:n,+ 1 t force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kept from od w (8 ms8tb;g.e:egf2d n6vpm1bla7accelerating by a man who is pushing bac;6a dedpgg :7 1 bl.(fbn2wset88ovmmk 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 helicopter of mass M an ac37p kega1 vd+*wi d-hrceleration of 0.10 g upward.w*3r-pv 7g1dkh +ed ai    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 is9e 9keo ddd fb7e.,ab eq1nw(/ 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 x9d/ +o1gp3xug qg6 cxf axis, varies as shown in Fig. 6–37. Determine the work doux+x6po /g fg39dcqg1ne by 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 acts ldvoav8uf x lf*o5q9r8 /i*8fin 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 mass ody*gk.wnwu 97 f $5.31\times10^{-26}$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 increasi+o/u2/zo sp saq6l82n d:dsked? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required)(cximya-qr mfkt,is05) zzr.u m0nx ;t y3- l to stop an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar travelina 75 ,*-bkrxgtuf z,.lwy gxz3g 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 Nz(8rc p g;pkaw-cb+/ mspa :;v on the 8kp; vmscr:p/b( +gw azap;-c arrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s movd5ri1iy(of 6y es a fielder’s glove backward 25 cm when the ball is caught. What was the average force exer(yii6ro1f 5 ydted by the ball on the glove?    N

If the speed of a car is increased by 50u v+*cscir.6 4e.h /thrjheo/%, by what factor will its minimum braking distance be increased, assuming aljhecsoe 4rv/.h u t*6 .ci/hr+l else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a h h-0df;q b9rcqqve/- car’s skid mark to be 88 m long. The acciden;qe f qhh9 c/-0qb-drvt occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at B0utra3tb9al e *c0u 5ey 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 plub 3re t5au0t 9*ealc0ate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown x;lt(h ds.+s jn40x jnx)4hw zstraight up by someone who does 80.0 J n4s(xsh +ljt jx.dhn04; )zxwof work on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration ane5-h0mgc3.j*h(e4 dxg c ebby a single cabl( ce*0dgx -.aecn4h hgje3b5 me. 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 constant, k,g 2if77eha104t cns0li btl*x of 440N/m How much must this spring be stretched to store 25 lfi1 0x7 asi 72*h ctlg40bnetJ of potential energy?    m

  A 7.0-kg monkey swings from onex7 p4sr9 riz5dtfa 0c eto9k-- 8,azvh branch to another 1.2 m higher. What is the change in h r97a-xrezfs4 9t8-d5ozpta vk ,c0ipotential energy?    J

  By how much does the g vh 3y1vx*jscoy17 9kmravitational potential energy of a 64-kg pole vaulter change if his c37ms191yy ocxh* v kjventer of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 6uo7q;iw (ln:1o hc r(x7ejno k2w/ qv01. xtro5 km/h when it strikes w0lxkovqo wn(oj :o e .q;7 1(hxcr2t7uin/r1a horizontal coiled spring 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 ar kk hln38eo(j29;tjt 2.10-kg book from the ground so it is 2.20 m above the ground. What is the potentiak( ht le kjjtr3o9n2;8l 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 climbs to the tksyc1x mk)n ++m6z4lzop of a 3300-m peak.mn1sk +kc6xl zzy) +4m
(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 hanu-0uld dj*;q yxzo9y /gs vertically next to a ruler. The end of the spring is next to the 15-cm m0 ydou -juqy*9zlxd/ ;ark 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 h 9tz8u(e9f6 2jy(hyq unm )bcrunning at top speed (5.3m/s) and grabs a vine hanginy8 9t6jn(f c)(zuu ybhh9e 2qmg vertically from a tall 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 ):.v jznc/ s2urm9geh 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 frictionlesbkk dhrj *,p+5s 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 7 np)y*rz updr3 )9uzei3 isf3kinetic 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 center of mass 2.10 m and cross the bar with a speed of 0ns) )pu3*r3ryzfi7d9 ei z 3up.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically up8utre ; c)yz)uward from the top of a platform with aet)zruu8;c y ) speed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

  $\text{A projectile is fired at an upward angle of 45.0o from the top of a 265-m cliff with a speed of 185m/s. What will}\\\text{be its speed when it strikes the ground below?(Use conservation of energy.)}$    m/s

  A vertical spring (ignore its mass), whose spring std)ne -p pc.u7af2 i5tyiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it 7dn f)-ay cp.eu pi5t2give 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 loope(:g yim7uinv9*brfz(z o q 80cd track shown in Fig. 6–39. If the block is to remain on the trac zuzf:y((vgobmcni0i8q9r7* k, 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-gu .wtiv lfm2sar5l(vw63 *x2osg6v spring (spring stiffness constant k), Fig. 6–40. The block is giv- w2lg5r2(*6mv luwavs f osigx.3vt6 en 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 bridgfochis;. +bc,e. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Cif;.coch + ,bsalculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged xcqz)3we5g: d up to point 1 where it is released from rest. Assuming no frictiong d)5c:x3q ezw, 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 angle758 s dwj.)mi:z lc:rwod oq2j 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 spring2:g l6cikys:b to be placed at the bottom of an elevator shaft. If the elevator cable should break when the ele6gb 2sc:y:l kivator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up4;tyt;c*9grl-skupj, krz * e 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 m1eae8stj;bslb sz. r d3 s77a,ass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this collisionabtj,7e d3.7re8sbs1 sslza ;? $a\times10^b$ J a =    b =   

  A 21.7-kg child descend4zz/lrmseni)cczc2 dm -(* .zs a slide 3.5 m high and reaches the bottom with a speed of 2.2m/s Horlc* e/nds c4iz2zm)c-( z mz.w much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides dof) fg:3mz0 xtu/b1 tv/dt*qakwn 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 abov2; 6nbrtq8 or8df3f w 9ujd6khe 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 bounces back to a height.;r *ryx n:ltc of 1.5 m. x*n r lctr:;.y
(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 k/-oshmx n0t )floor 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 /-osxtmh0k n) speed of the crate?    m/s

  Suppose the roller coaster ix: qb o6 ,us2q;yl-pqbq5u)ycn Fig. 6–41 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 qb5 qy:p,y cul6x2;qbosu-)q m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady upward 18.0 (smq(g*znox; 4 svof( $^{\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 horizontqao:o-224wc lgf7rs o al 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 friction between thsrwgl 2 -2oo f:a4oc7qe block and the table?   

  A 280-g wood block is firmly attached to a ve*f j, k(tyzt9w*n;ttv-t *buwry light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficie* *ktf( ytztb-*t,9tuw vj;nw nt of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the spac 5cfhx+mdp r/4e shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its mf/ r4 dx5pch+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 apoetqn57v k2n-d* +c3k7 y j lxi6y1kb 315-kg piano to a sixth-story window 16.0 y5b- jvp 7*k7qild ntc2 kok63xen+y 1m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what mu(tereom4ys0s +k(a 2) van3 mxst be the average force exerted t ae(a02resk x n+)s3y4mo v(mon the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates nvp1vgvay58bqg, l 76 from rest to 95km/h in 7.4 s. What is the average 8 5lyvvn6ggv,pq7b1apower delivered by the engine?$\approx$    hp

  (a) Show that one British s)1ok1fbt jcr14k-o bny/gu; 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 in the form of “k)4eiu q fnys4bpy3 x3hzb+o0( .v7grkilowatt-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 sluxn7oj-l7f +lows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately ujn 7+xl-lo f7what 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 1.wm2v(s5ad 2cp0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this motion t61o as:+5y:mu fxgdp wakes 1.5 s, what average power w xm6w1p:sf:agoyud 5 +as developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minutehk/ 9jf -y5som+gps ;atew6 7,n hq0kv through a height of 3.60 m. What output rating (watts) should the pump motor have?syf/kw0 ;ah qjt-,vs ghnk6p59 oe 7+m    W

  During a workout, the football players at State U. yw;3/s e0ri8;d2/akklwhnx n+;n7vx agfkc) ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined at an anglew7n/keg)8hnnl0 +rakv sf3x d; xwa;ci/ 2;y k 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 6.0)sh 3e v)yo9gevu+i 8y $^{\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. f3ov/ brn,lzsm w/p 4euu;i) 1How steep a hill can it climb at a constant speed of 75km/h ifrwnouvbpse41 ;zm l,)/iu/ f3 the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepowe toy,e;la01wdj* mo )er must a motor have to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of fraj1eoty*;lm w,de)0o iction is 0.45?    hp

  A bicyclist coasts downause;3gei7,ayk,g)n 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 cam:ls2f ia f:+;dx;d /tdi aa7wrs have built “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming intoa s;7i wa2i:mdf dt/alf:d;+ x a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is ejp f. 1yh+oa6lcnjm- rf6ez 3(+pk6 y10.0 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, he +zca(16pnfk. m+ro6y6j-yjfel3p 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 ju k+y9+ mu5n gfnuc 7fioz-nv90mp (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed dido+mcu0f+nz nu9k79gnf -ivy 5 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 8ionlc +4 +fu.ue wvqwi/w31 fwithout friction along the looped track shown in Fig. 6–39 is to remain on the track at aqw4 fi/3 e.f o8cuu+ilnv ww+1ll 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 rug,7(k7h ai k )hrir0jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, b0gkhkr(r7,i r u7)i haut 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 cord of length L whose other end is fi + wym-kv-wg;kxed (Fig. 6–4-yw; mv+gk w-k3).
(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 37,bgpwf6a7n +2rjfwy** f sw(f 00-m-high mountain. The climb is made in 5.0 h starting at an jfp,7w( ay2fb*wf* n+6grswf 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 p tb4rw4l0pv4 1 6dk0pgg l*qfelevator 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,z7 ds+8jx91xf)y iy uv000 people per hour. If th)xy7vx+fz1du j 9i 8sye average lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and hv,qz3i5xbel.;u sbs61n 9/mtto(xyfalls vertically 81 m before striknv sl5 9e3y/x1ob.x s;himb6t uztq ,(ing the turbine blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical loop (Fig. 6–44), thew1+ 3d:uns w7zab387ojbit ys 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 th7yn7t1ws dbi3z 38+jaowb:us e loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly ig/ z5qmfs ii26nto work, how high could an 82-kg man climb a ladig65/ i2fz msqder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward angle of 45.09slk-kbj , vt,5w6ang $^{\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 scacg+ wt4y m/5qo4t0w0i7aw pg4xkqvf, le compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what dockf/wiv40 +7 q maqygt5t4wp x0wo4g,es the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings c 0b t9ytvxf47out over a lake (Fig. 6–45). He releases the rope when his velocity it7c9 y tx0bf4vs zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5.0 m in p6rrskvr t8j z(zg)yo,ap9+ 6 9.0 s. y +p gra9ov( tzpzr6,)rskj68 What minimum power output was used to accomplish this feat?    W

  Some electric-power companiesgg-t r -.k( ru vt*oae1q:fik, use water to store energy. Water is pumped by reversivu:kg- rtiqgo-*ark1.tf ,e( ble turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in half. ;:*ubbzsi: 0 yutw-rgWhat is the spring stiffness constant for each of the two resulting sprub wg:rubz y0i :;*-stings?   k

  A 6.0-kg block is pushed 8.0 m up aoz;1s3w s4ethe:+pn b rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from u:t ik6vl -z/yk m9pu635km/h to 55km/h in 3.2 s, how long will it take 6pvktlk6yu-z9u :im / 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 (thewdhl9rybj9v5u 1 zgl.+ .r ;am “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patiengv;m9a +ry5l urw9 bzd .l1j.ht 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 distance of 1hpin; *fwhp1500 m, what was its velocity when it left the volcani*hp1fw;h 1p no? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a rate of 95kg/s v2sr qpzc:(edl002 qg(a) If this water wheel is set up to provide electricity 0(2 cq :lrg ps20deqvzoutput, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s