In what ways is the word “work” as used in evr2y l klo9xn4-ktix)5xwrib)8w 3u(ueryday language the same as that defined in physics? In what ways is it different? Give examples of both 35-uro kyk4(wxrbtxx9iwlui 2)8) nl.

Can a centripetal force ever do work on an object? Explain.hbmrsl+ t(:j z*. xh;btti-zm lq6f92

Can the normal force on an object ever do wor ijfkd*dl/ay 8/ 8t8exk? Explain.

A woman swimming upstream 6n t/k5o1nady is not moving with respect to the shore. Is she doing n61 tao /dkny5any work? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces alwayjz9u+b hyms5kw38y 6 ns negative? [Hint: Consider what happ5kshbz9y wy+jm368un ens to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid walvv-ofe5t*swq8+z / q nl even though you are doing no worfo* w zvq+e 5t-ns/8qvk?

You have two springs that are identical except that spring l is stiffer than jnrct , rp)5pqle7x 3qpd-: -cspring 2 ,-7cdp 3 )x ne:t5lpj-rcrqqp $(k_1>k_2).$ 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 forccac8 5 ddm uw:gm)3g+ce on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts fgdc )accumd 5m+83:gwrom 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 doesk /wco2p6ym1q82qbc t your gravitational potential energy change when you jump p68 2ccbwoq12/qky tmas high as you can?

In Fig. 6–31, water balloonpp9va q0he6)zgf; eu, s 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 impact? Ignore air resistance.he; vpfq z0,ega6u 9)p

A pendulum is launched from a pointax;y t5e 9wf(q that is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is direc fqeyx(w59t;ated 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 cv*l , p.9ny:v(q pqtnoompress the spring by pressing down with your hand and then release it, can the spring leal no.vpqyv*(p ,qn t:9ve the table? Explain, using the law of conservation of energy.

A bowling ball is hung fro6()2uxawvdvt 2cj, m:4lv r*nd x uux/m the ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands ud2uvv j6n4a wu*x/x :)dxr(c tlm v,2against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the 0hq8;lipgwx9kfjw jy33 z; r6 gravitational potential energy when water at the top of a waterfall falls yj8x 3jri ;zg kh9f3qw;pwl 06to the pool below?

Describe the energy transformations when a child hops aq 3x ;t2e;e.,dm k+,sftdni0pbalfe; round on a pogo stick.

Describe the energy transformations that take place when a skier startsiy-tl fm(h4v7 skiing down a hill, but after a time is 4lvm(hi 7 -fytbrought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from)) k*r1l.g(fars bbnb 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 friction, and (b) there isbkarr ) 1(bf )s*gnbl. friction (deep snow)?

Seasoned hikers preferd0 5 rthcips59fhxbk3i d)1s 0 to step over a fallen log in their path rather than stepping on top and jumping down on the other side. Explp50k i3i)9ds 5rbxf0d1h tschain.

Two identical arrows, one with twice the speed of the other, are fired i.elgr 7mo5 bj,h91o h lhs1m0ynto a bale of hay. Assuming theh7 0 s,eoll. 1bhryhjmg91o m5 hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple sw)bvpd6+ 4iln t2m ex+ i((qfvqv f4-oxinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain omxb4- () pedv iv2l6q4+fqnfi+(vtxwhy a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a u irp05uk g5ovp,/vzck+b8- cheight greater than its original hekbcpgzv85 c p0,5kuru/o-v +iight? Explain.

Suppose you lift a suitcase from the 6joc l9obz,m9floor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift b9oz9o cm,6lj 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 the powerh8:dkvxo2d l3bm *z)q;pezt7 needed rather than the work.

Why is it easier to climb a mountain 1;dvw+fqwtja e 4(nby;o);k qtz x s92via a zigzag trail than to climb straight uet;j;a + d924x )zqyb;k tq(wfsn 1owvp?

Recall from Chapter 4, Example 4–14,fmnioxtvj35j .7w0 c2 ;ub an: that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy c07xt bc:2j3nun;v foj.ai w 5moncepts.

  How much work is done by the gravitational force when a 265-)he ot8 6,jkwckg pile driver falls hek6 o t,cjw)82.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 ::fw5t3i2 hp1ti+4rmwxwg9re( m7 jpcm-a xf m high. How much work is required? jxtxf97rrfgww mp32a+m5m t1:hc(ii w:-p 4 e   J

  A 1300-N crate rests on the floor. How much work is required to move it at cons:c,a.un) k igatant speed (a) 4.0 m along the flo)k aga c:.,unior 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 crate 10.)qp1rjp ,z3o myvwtz; : rjnxl)-6t4r3 m across a rough floor without accel)y:r6vp-q;4 nr otpwtmj, )jxrz zl31eration, 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 rat+ jcp23lcu(u1n tuf- bax 2 pp7vgl);ve of for 7.0 s. Find thu ;2javgu7 f-p2x 3bp(t 1ullccp+nv) e net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. Ho gk5c.d g7)wtsw much work is required to stack them one on top of anotc gd)t5.s kgw7her?    J

A lever such as that shown in Fig. 6-35 can be used to ad6p4o yg/ bx*zt2 3jbliff objects we might not otherwij 32zpdyo/*ag bt b46xse 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 mk8ssp,w6savqxty h4 .w4*h4h 5xh 3ts down a 28° incline and is kept from accelerating by a man who is ps4s6*,4wq h t yh.xa k3vh 48tshspw5xushing 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 helicopter of mass M an accelr1(pyc nlnok(ej ( fs 0rqxu73r)ea+)eration of 0.10 g upward.)(ecpjefar (rk3syn(7q 1)l0 xn o +ru    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume the distance axis is linear and thw-owtx /wh+ x/at $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as shown in Fig. (sw8xzu2l xkrh0)ygui54k 6 a 6–37. Determine the work done by thi il06k x )wukg(asyxhz5r u824s 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 hd(3wc0 j am:/y8bzjion a particle 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 moleajy/mqom053o)q s zngvsq 3 h.0u4ck1cule, with 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 r vxq v/rjn;4:r.b94gk3k fpospeed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an electronk+w 5mg2qmy36-* c, nufs e;)tiehrvn $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 yy(8hphh-m3e)9u p6 jlue;a,p ykp t 5done to stop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from aqyhdx *. +eevt,yb wu-nud*01 bow whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed ohx-wn1e.edq*,* 0 +utyd buy vf the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward2eysbm7ct1hz di e b;l4o*b*( 25 cm when the ball is caught. What was the average force exerte c** 7d( 1byb4h2lm;ozstieebd by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will it+ ob43 urlc2r00bq enhs minimum braking distance be increased, a2reoqc+3rubbl nh 4 00ssuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a levelu;,cje0 rwo rwxa7y :7 road, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use, 7wu0eoacyrj:x7;w r 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 reaches the pwsul5wul o 47oaq .-(xlate, it may have slowed by 10%. Neglecting gravity, estimate th-l4 o wa( 7lx5wuousq.e average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown strbd cntl-rl 49ea.1fga b.4h0aaight up by someone who does 80.0 J of work on ra940l. ac abnf-dehb lt.1g4it? Neglect air resistance.    m

  A 285-kg load is lifmp7m6 7c uh:p3sakt ,dted 22.0 m vertically with an acceleration by a single cabl upa:6 m3tcd, kp7mh7se. 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, eimzqp,w 38rtt cu8:6 of 440N/m How much must this spring be stretched to store 25 J of potential energy? 8ietwt:rm,qp 8z u3c6   m

  A 7.0-kg monkey swings ft rxdkzb956* xqh4:v.y uro 8srom one branch to another 1.2 m higher. What is the chan9 oux6b zst4*yv:kd.5r8 hrqxge in potential energy?    J

  By how much does the gravitational potentk-v j. 9irinc1/upd l:w jnl+3ial energy of a 64-kg pole vaulter change if his cente-u9n+ .jrcdnvl :i/lik3w j1p r of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface ha:,xvcq n3+l vg*z m sby;-f+vus speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance nv:f,q; gyzv+ l-* v x+msbu3cof 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 bh26g p68tgswcook from the ground so it is 2.20 m above the ground. Whagh c8ws6g6 p2tt 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 climbs to the top8. tn wc/bd0ub of a 3300-m pe 8cwd. ntu0b/bak.
(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 ve y4ld2ch qc19rrtically next to a ruler. The end of the spring is next to the 15-cm mark on the rucl9rqc h21d 4yler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a vine haqi(g(10o)h wk.hwu b jt1sd :tnging vertically from a tall tree ioit qw0 kdg1t:u1wh)( .b(s hjn 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 fricti1k0* cfsc6rr ionless 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 f 4s8:( 2rfj c7 /nen6okxv2np;wg ooxprictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into gravitationvd i4 rudmo9:c2ey47z al potential energu dd:c7z4 mvi 9e4or2yy 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 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward frozwlo89xk3ikn l d-x66m the top of a platform with n9wx zik3-dl 6k xo68la 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 (igno11lr1 2 4nldc n r4wcwx9txvv:re its mass), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when rel clx d1 :1nrcwlwvn14 tvx24r9eased?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction a1hs)4f6c/alzw p5wdilong the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius iac s wiz6)/dhlf 4pw15s r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spriiuoa- *t,f pg/ng stiffness constant k), Fig. 6–40. The block is given an ini,f-got*u/ap itial 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 fromtc*c az03r8fn a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calcula rct*n 0z8cfa3te 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 up 9*zdgpi dcmim(k/. 3mto point 1 where it is released from rest. Assuming no friction, calculate the speed a3ik g i/*.ddz(cpm mm9t 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 a)fiieeo.34q 7h1z ko*ixw)ykxh0 7 uhn 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 uf +vxbzn97d gptu3n0+bw7l .9jbyz/ placed at the 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 b. n3+0zd+vgx9bzf/jtu7nybu w9 pl7 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 up h,c9:e1wrkhfc5 a:pqk*+e 1 avl 8bud6j 6rjla 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 ,dxrf jxb 19/ol1nu+es 8yj;xqwa k.zu3 xi8)kg and traveling 95km/h in opposite directions, collide head-o)s1i1+ / k.joj,89f r 3yd8xuwxnezax lqbu;xn and come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches th wdti,+gohh622v3cw1r xu4jh e bottom with a speed of 2.2m/s How much thermal energy duwdu+ohih vx 36,2t r2j4gch1we to friction was generated in this process?    J

  A ski starts from rest9 /3k;kxu mnol 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 tre *5( af1qipe 6o5n9d kk:iasqma(*o bmddm; y0e 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces bax -r6hc, yi1fg/ xnr*ju;6tv lck to a height of 1.5 m. x *r6/y l,vuf-txnir6j1;hcg
(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 floor wix ujk inl/*5e/ pik8az0 x2m6ith 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 sp5/*nizkijel xpu/x2mi6ak0 8eed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes az;us 4-t/tk)zk2y zxpoint 1 with a speed of If the average force of friction is equal to one-fiftz zx2tkz;4a)tk u-ys/h of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a 9m /tvz7//.a canuulhk+ (i(n3ozkn nsteady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very 387c qlovk4sv light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring73 kvs4vqcol8 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 the block and the table?   

  A 280-g wood block is firmly attached38-h*twytlb)jnf (p w to a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far b3y )t(8jw pnw*btl h-feyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle us+2uclagm ij*c370p8llu dlo2ed 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 landing speed have been in the absence of air resistadm8l2l+ p7 c*uig03ojlu2cl ance?$\approx$    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-story wins4yf8 amr of q 076udbo.-hh qsjz40bv26qe(jdow 16.0 m hm47ov fa0 b yjjq rq4b6u(oz2ssh-6f 80de.qabove?    s

  If a car generates 18 hp when travek0tp(uft fu-s5 r, od)ling at a steady 88km/h what must be the average force exerted on the car due to fricprs0 u5-otd ,f)kft(ution and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7 vx -e,48q;eb xm2tx bhlp.q(n.4 s. What is the averae; l(x e, tqpx8-h4nv2.qbbxm ge power delivered by the engine?$\approx$    hp

  (a) Show that one British horsepowern dxs2+ .y c1/df*yvdu$ \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 fore.xmc v,vnv9;m 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 abouj *g-pisx q3u74 l2fsgt 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the cag*iss-4l7pfq j 3gu2xr traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor w+mwvsbf2 -*u do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this motion takesofas +h)- )7(dyjf*vvuj n,f j 1.5 s, what average power was devv )nfoj+jfs*-dav)u,(j h f7yeloped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute thx6 hfu41uld/prough a height of 3.60 m. What output rating1dupu4h/ 6xfl (watts) should the pump motor have?    W

  During a workout, the football players at State U. ran,de-m/ hfda6ex-oh;g up the stadium stairs in 66 s. The stairs are 140 m long aogxeae/hd --,d; 6h mfnd 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 cyclftad.f( +w .poist climb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. How steep a hill can euoij* ymp s/4b+5r,8u96bumx sau*k rp 1-ieit climb at a constant speed of 75km/h if the frictional forcesmu ymai bi5s /-pkj1*89+osu4p6rre*u bux,e add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg box along1lrq2 z:r;tc8 r9.rv2ci. oy n 5zkkng a level floor:nn2.cytzqg5k82l1r zr;o r .9kvrci at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.0 +or3yqa aq*ehit(3) z)./zrvf gux f- $^{\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 b dtf8ax eescas(ly6+2:g 9,druilt “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds bel26ag9,xc f a:eyed(8ldrss +t ow 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the ground, and the ry/ow)+mh z6a7pza4 x yemaining four shelves are each spaced 30.0 cm above the previous one. If the average book h4) zxhyz7 w/ +ypaoma6as a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Olympics 9oo2ktlqhvy/sk69d/ 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 tra vkk9os ld/qh9 /6ty2oveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the lt:dhq(0sdjx w7/7tdwooped track shown in Fig. 6–39 is to remaid7tw7dqhx sj/tw0 d: (n on the track at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft without hisb,xjb)s lr+c 0 parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s es+r)jcl0xb , bstimate
(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 horizontaln 7ak;q+y:o c3gevr );otkx-n cord of length L whose other end is fixed (Fig. 6–43). k+c a)t3;o-nrvo yn;ke7g x q:
(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 tof6uhx4 xlp20: /6n+cyydg z hrp of a 3700-m-high mountain. The climb is made in 5.0 h st:rg ypx4 +2nz dcxhful0yh66/arting at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m fvkqk-5qinh xjy; 1;+z aan20zs(r0gabove 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 canop7 cy ejo21;ancjt-gp .ada. f 10:iw move 47,000 people per hour. If the average lift carries people about 200 m (vertically) highe2:.e1yjj0p-anwacafp ;oo 1d 7t icg.r, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at thr 1c lr* 3:ckqr1had8je rate of 650kg/s and falls vertically 81 m before striking thkh jcq18a*crr 3:1ldre 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 c5 se)kmn pv;/woaster with a circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the5 m/;pks)ev nw bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly inte4+h1 + y(pxxx8qmdlfo work, how high could an 82-kq8xdmfelh + 4pyx+1x(g 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 g9: ny 4gs ,ltaomfto9x.-wk-at an upward angle of 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 scale compress.3ojzhxlt 46 ces 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 does the scal43z6h. xl tjcoe read at its peak?    N

  A 65-kg student runs at 5m/s grabs a a.k 7r zw,mwd.+sy)g3uc )n mtrope, and swings out over a lake (Fig. 6–45). He releases the rope when his velocity is zero. wscwduyt .,3zr) .7nkg m a)+m
(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 clnipz(m uysk 928c-s /simbs a vertical distance of 5.0 m in 9.0 s. What minimum power outn9s/y(- cus2p 8mzsikput was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumpex0mn3cks,k.g,m )s(cu1qw v dd by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 s,3xk,ugw1.n0md)v(q ccs mkhour 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. Whawa-r j 1t)i9 t((8xxzqz(x hypt is the spring stiffness constant for each of the two result (za)it tj xx8w1(zypxh-q(9r ing springs?   k

  A 6.0-kg block is pushed 8yzw+4odsgb1 1 .0 m up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 s, howkly-x2 jyol)23cs 5ja long will it take to accelerate from 55km/lsao -5y3yjjc2)x2 klh to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patieis(-e cc)s n 7xpqg*u.rh us64nt walks on an inclined treadmil c4.ss)hp7usc * -(rxn6geuq il (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a distance e*w n8ftld4 8 csx*cla7p76oqof 500 m, what was its veloci4adf lc6c8tpq7*xeo7*s8wnlty when it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a rate of a ,jwy:d e(ta295kg/s (a) If this water wheel is set up to p:2yw, jetaa( drovide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s