In what ways is the word “work” as used in everyday language the saxxb10nw,5ej a.x u.wrme as that defined in physics? In what ways is it different? Give ex1bx 0n wr5x axju.,ew.amples of both.

Can a centripetal force ever do work on an oh1s0+* zxmzg2adur pac:+te 2bject? Explain.

Can the normal force on an object es n5+wp cu-4+jj+hq) yr ub umoj:91eaver do work? Explain.

A woman swimming upstream is not m7.+aefeb,) k lu uwji+oving with respect to the shore. Is she doing any work? If she s ,+l+iekufe )bj7 uwa.tops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: 0xs+2dec (s;r t4eg6 ;uimqnp d0d j7bConsider what happens to the dishes when you pull a tablecloth out0n(r 7d;dbj+46c;s0x t es2upm i qdge from under them.]

Why is it tiring to push harp; ,y n dc.-biures5l9d against a solid wall even though you are doing no work?.,l -;ecyin 95pudb rs

You have two springs that are identical except that spring l il)le/ao+ , fyzs stiffer than spring 2f)lel ,ayoz+ / $(k_1>k_2).$ 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 consta:/.c 6 dfwni mb dzg 0gfn.c2zag(z,6snt horizontal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and c /f wn( g:ad6zz,s. d gz6ng0cim.f2bby 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 gravit e)gjfd-ta :;fational potential energy change when you jump as hi: fgf-j d);eatgh as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building,.u:fd 9zutb qdp-oa7 , all with the same speed but with different launch angles. Which one h utbquo9. d,:fz7p-da as the highest speed on impact? Ignore air resistance.

A pendulum is launched fromn6jysdp4/,mymj)y f 2 a point 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 3.0d ysjpm 2f)/yny4m j6,m/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 compress the spring z,y x x 3+t1jrduzp8v;by pressing dowd 1 zjp8x,vxz;ryt+ u3n with your 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 (dnhtsjnh1e(tm z :,z4c;zv .w *lcu ndv06 ,q(Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instr,tnzzjslw0 4.hn6vvc * zd(n 1 mu,h :(ect;qductor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy whenwcjv9, knoo 53 water at the top of a waterfall falls nkv9 5ocj3wo,to the pool below?

Describe the energy transformations when a child hops around on a pogo stickzo/0znq;e9 b-ktn0q)zv sqx40o ud e+ .

Describe the energy transformations that take place when a skier starts jwal415ga .tjxjkjq;q(1)tmzz 9(zhskiing dowazg4jtj x9(q.hqkzzamtj ;j5 )11 l(wn a 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 top of a hill of heig dd)bgwb.j9ayyv:s-,ht 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 is friction (deep jbdgdy.s)byv,w9:- a snow)?

Seasoned hikers prefer to step over a fallena mch,sr +0i-.zglmr6 log in their path rather than stepping on top and jumping down on srag, hc- l+6zmrmi 0.the other side. Explain.

Two identical arrows, onbjcuklut7 / /if-8.kxe with twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constanfuuki -xjl/ct.8/ 7k bt frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swingi,o7vp w1u7pg yng pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into acc7ov 1uw p,7gypount. Explain why a grandfather clock has to be wound up.

When a “superball” is 6jt*i:x i(cpy4 xvet2 dropped, can it rebound to a height greater than its original hex2tyv*e6i c:(jp x 4tiight? Explain.

Suppose you lift a suitcase from the floor tc:o8(bu sa +l5yup2vk- dz8xto a table. The work you do on 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 table, and (d) the weight of the suitx:ka vu+88tly szbc2- o pu(5dcase?

Repeat Question 22 for the power neeje05bv 1(:a)(koh)i)eslfm qk lz + / *rkflccded rather than the work.

Why is it easier to climbf0q9q v 1n ll(:7nxvym a mountain via a zigzag trail than to climb straight upnv f1ll v7 myq:09(xnq?

Recall from Chapter 4, Example achetq 4(6 hcj*zl m674–14, that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). Bu7ac*6h(c zj6he4 m tlqt 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 gradvp8sreh v25/c;-ukj vitational force when a 265-kg pile driver falls 2.80 25-vukds/ pc8 ;rhjvem?    J

  A 65.0-kg firefighter c g*q d4w :l0p8p+mihnglimbs a flight of stairs 20.0 m high. How much work is requir4qh+l8g p*mpn wd0 :iged?    J

  A 1300-N crate rests on the floor. Ho:g,r;i(l b/jiwsxwx wp75kmr;lnmcvj i8558w much work is required to move it at constant sp/;m;rnrw:ijjw 7mgv8 lbs8x5 kc5 ,ii5x(lw peed (a) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the moveiw.ap i6i.tnmz. g, nf -buw2k5ks/63 )r hgimrs do (horizontally) pushing a 160-kg crate 10.3 m across a rough flu6k3 ,gwi2 bn/igm-m5ikwf as6hp z ti).rn..oor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force acry .qd.j42a h7sbcl0qross a floor at a rate of for 7.0 s. Find th. yrq aj2l4db7 s0.hcqe net work done on the box.   J

  Eight books, each 4.3 2-ad3t w +2bvxpp9ru,s+ guxvcm thick with mass 1.7 kg, lie flat on a table. How much ww t xvv,9da2u r+sug2 3p-+xbpork is required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects weyo3xl4 ft 8tu r3nld9- might not otherwise y-4l to3nlu9 3tf d8xrbe able to liff. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths ${\iota }_{\mathrm{I}}$ and ${\iota }_{\mathrm{o}}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kept from acc )e)ewqanv2*o sdyt0 7elerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate: we0y) n7a) o*sed2vqt
(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 accelera a7vqvf(w (*abtion of 0.10 (7 *wqavafvb(g upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume the distance aymnb;jx.5k0 e ,3wgbc e7r sq+xis 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, varies as shown in Fig. 6–37rl.b/ocag94 m3g+ cs r7vay9 b. Determine the work done by this force to move th9bbg gmyc+ar lrc43s. 7 o9/ave 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 in the k4 hq5 .g3v 9zs+jptgud8q7*g5qxtik $+x$ 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 massg2:1l7qggxvh0 ryk)hnnll9) + qbj .d of $5.31\times {10}^{-26}$typically has a KE of about$6.12\times {10}^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an xg 2dx+)jt6q qg*uau (arrow is doubled, by what factor has its speed increased? $\sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is reqccsm:wc 2p+cqv6bpt,2x: l 0zuired to stop an electron $(m=9.11\times {10}^{-31}\mathrm{kg})$ which is moving with a speed of$1.90\times {10}^6\mathbf{m}\mathbf{/}\mathbf{s}$ ? $\boxed{{\displaystyle a\times {10}^b\mathrm{J}}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar travww8:iteir/lau 5n.09iq8vn u eling at 105km/h?$\boxed{{\displaystyle a\times {10}^b\text{J}}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average force of 1w858 i;lyf auy10 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it leaveswfl;8yua 85 yi the bow?    m/s

  A baseball (m=140kg) trai*g, .va ozy;7ict )xfveling 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the averagefg7zx*,;cy)vit.o i a force exerted by the ball on the glove?    N

If the speed of a car is inn 9frcz1u/;f bla i,b/creased by 50%, by what factor will its minimum braking distance be increased, asficl ra 9,b/z/;nf1ubsuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measuun7 4okqy/s9tk)c 4q bre 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 these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the7t n4by)ckqo ks/94uq car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By qv7y92wfc (*uah i ;lmthe time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average fa2 *vc 9iu; wylm(qhf7orce 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 bnwcv):* b(dxthrown straight up by someone who does 80.0 J of work on it? Neglect air resist*:w)vdx b cbn(ance.    m

  A 285-kg load is lifted 22.0 m vertically wit 7jrkz c52bk9quj*p3tf+4zdv lch/y/h an acceleration by a single cabq* 743b9vzd 5+c2f klhputcyj/rk / jzle. 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, of 440N/m How 7x-wkhx:+kov 57j( fukm5gtduo g s8m zu,-g/much must this spring be std gkthk5xog (u x-f +m/g7:wk58us-uzv m7j o,retched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. -brqf 1nu-4pwWhat is the change in potential eq4b-frpu w -1nnergy?    J

  By how much does the gravitational potential energy of a 64-kg pole vau /, jkboz5tm1vk3wi (elter change if his center of mass rises about 4.0 m d(/vt1w5ik bj, ezm3okuring the jump?    J

  A 1200-kg car rolling on a horizontal surface has rp07l ;b x ae2.lf):q 8syyqiispeed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffnesss ;)ialf 2qxlyeb q8p7:.ir 0y constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it isrpc9v cor-m6i iv b7ew+) )frnul5gi3kp9h(+ 2.20 m above the ground. What is t5ip9e )lvhwc+-r6 i+9pn )vkm7u3( rbfcrioghe 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 top of a9 5ui. q4ovfp )z(yegn 3300-m pynio5g)(. 4u9pfq ez veak.
(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 hanegw: yuqs9* ,mgs vertically next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is nowmsywuq:* e,g9 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 /7ggf2w5oc6j:la 3jm owm9 5 - thzmwoa vine hanging vertically from a tall tree in the jungle. How high can s /2om7w:ga-gw 5 fcoj69l5th j3wozmmhe 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 :* /m)-ddp/lgm*-axz4kz ck qey cte2 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 up5p iq tc5t7a-*/hchpm a frictionless 28.0${}^{\circ }$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into g )m*yocgjyfp13.o +zvravitational potential energy without the aid of a pole. With what *yg cy1fv)zm.o3p+ ojminimum 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 from the top c 6s8z6m-( 1 zl4aqjzpmh(onbntp0n 6of a platform with a speed of 5.0pajmm z(p8holqzc n4z06bn 1 -n ts66( 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

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

  A vertical spring (ignore its mass), whose spring stiffness constant is 950N/h)q 2f;u7a lrns u2))mcz.q aom 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 released?a )qm;)7ohz scf)uq 2runa. l2    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides withojmoae z ; ok74nau6 )cxp+f5r3ut friction along 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 is r), from eu34 ; n+ac5j7kax )ofmprz6o what minimum height h must it be released?    r

A block of mass m is attached to the end -ppcx9h6 av/ stqv0c 0of a spring (spring stiffness constant k), Fig. 6–40. The sh/t6pcx cpv09 q 0av-block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a buc ig5 nu -w+,vll4ur7mngee cord whose unstretched 5l mnl c4u,-w7r+i ugvlength is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragg-qzes kua) p55ed up to point 1 where it is released from rest. Assuming no friction, calculate the a- 5sep5) kzquspeed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12ua4vm - *utwxd )6v,p9tj 1krq 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 spj8 5;p,kok i8tfwc 3ofring to be 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 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 passen5wc8f oo j;pik8k3f,tgers.

  A cyclist intends to cycle up a 7.8rc:(hb fdz/p rkg9*c( ${}^{\circ }$ 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 offcr-afk,)u u5 mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is prod)rfku 5uaf c-,uced in this collision? $a\times {10}^b$ J a =    b =   

  A 21.7-kg child desc(pcy vvvy: ;8rends a slide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to frictrp8vcvv( y:; yion was generated in this process?    J

  A ski starts from rest and slides downe 7(h.d yylhug2*yf 2u 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 abovd,r n34lii+pne 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 vk7eg/f k,hux28htw,uf d(h ( a height of 1.5 m.uf7, kdh vg ,tk/8wh 2ux(ehf(
(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 wuza(dlm1phlc;.zz ( 7xg p8b52vr.w rest, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for thcv(l7b;p zla8z g2w.. prwum5 dz1 xh(e next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coasteror-xc3vh 5 l5 jli, uz4yw8,ap in 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 tr xrpavil,lw5,o c- hz3485 yujaveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s re7ki+)* e8 n,v4nigu g ddgxmq,aches 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 atta3im7onv b9q)t kc2yk +0p ary*ched to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stoppingn +yqv 7k) 0cp*oyk9mb2tia3r and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attachexsyn41: hn4od8ittbvq ;5pr 8u-i l1fd to a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficip1yosdr 4iq5n;i81un-x:lt vbt8h f4ent 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 fork ;y)*ub8czprjt sbtjn 8s52ys/zdxc+9)lf 2 the space 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 b +2zkl;2cntuz*c) 8sxbfd/9 y5) 8tssjpy rjits 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 pi iw2kwj r*tvz/ 1wn);wpfkl.; ano to a sixth-story window 16.0 mv1)*/ .zwkt ikj;w f pww;lr2n above?    s

  If a car generates 18 hp when traveling at a steady 88 y, pea0ys27dg 0cpmbe),t ttipn8h62km/h what must be the average force exerted on the car due 8e pp2e0,0t)6tth adc,y2bms g yip7nto friction and air resistance?    N

  A 1400-kg sports car accelerates froml01ffe9atsg6tv8m+ zri j 3 g0 rest to 95km/h in 7.4 s. What is the averagaf06jf8lg3t0 tvrems + 9gzi1e power delivered by the engine?$\approx$    hp

  (a) Show that one British horsepoweigf* ldx4k/f- qebc06 r$\mathrm{ft}\cdot \mathrm{lb}/\mathrm{s}$ 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 “kilowatt-hogf4t s/lj5t5w urs.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times {10}^6$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?$a\times {10}^b$ 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 froy.vr exl6z m47s(:ytp thr6 z)m to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep txs)7e rvz6zmy(ty. :lhp4 r6the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1.0 h? w4cech k(cle7-0q+gy $a\times {10}^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this motion ta 0ayd)n0oun) or0j3 etkes 1.5 s, what3a )0rnndt0) jo0o uye average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per m 25ju*zpzv;:qag zt)sinute through a height of 3.60 m. What output rating (watts) should the pump motor ha*2j; pvazgqtsu:5)z zve?    W

  During a workout, the football players at State U. ranj0 :x ch8hjnwvp+9b d +y7e2sx up the stadium stairs in 66 s. The stairs are 140 +d x 7yshw0:8j+h2b9jcen pvxm long and inclined at an angle of 32 ${}^{\circ }$. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist 1mj,b2 m5 nvwah)yo kc6onw9tn*k, ( dclimb 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 hilmz aow3t-fj.); ezuy.l can it climb at a constant speed of 75km/h ifz .yfa3-te)j umzw. ;o the frictional forces add up to 650 N?    ${}^{\circ }$

  What minimum horsepower must a motor have to be able t x0ar, iyd2o2s4ddc i,82xe 57j crqqbo drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of friction is 0.4q2 07,iroxjsyrd824d5cb qx, icda2e5?    hp

  A bicyclist coasts down ;b3a2j/nac:auwx+ gp a 7.0 ${}^{\circ }$ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bump8lxxpl4wuz68r, vc4 puk;2 quers” 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 compressiowl4xl u6k4rpqu z, 2p8;xu8vc n 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? $a\times {10}^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off th i9ey /os5(pgxe 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, assuming the books a/5(ig 9y sxpeore 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 -qg0dpuc69l bOlympics 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 cd0g- q9u6blp at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped track1 h1v4vt1wg 3q)snkc z*g on:c shown in Fig. 6–39 is to remain on the track at all times, evenc31:h g1kgcsvw vnq n)*z 1t4o 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 aircradyilcrrg igj* 3/y bai,jew;1it,;r q)++p ,jft without his parachute opening. He landed in a snowbank3 ib;,jg;da1irgpe,j ,l* +t ijir +wy q)c/ry, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whoye3hc0t.8q q viyk:x*se other end is fixed (Fig. 6–4tv. 08 iycyqe*xh k:3q3).
(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 climb is max.6wpqxysrlh 4wwuj) : n e.+.de in 5.0 h starting at an elevation of 2300 m. Calcs 6x n4uhwwyrl..wxqej)p +: .ulate
(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 abo nq8l2wgih sgv9-9hug :ahe62w *6y azve a huge spring ($k=2.2\times {10}^5\mathrm{N}/\mathrm{m}$) 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 Calif t. yp*6e t4dras)(lliornia claims that its lifts can move 47,000 people per hour. If the average lift carries people aboutstayl6)ire4p. d(*tl 200 m (vertically) higher, estimate the power needed.$a\times {10}^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81 mr h se-1fuqn0r4:op (e before striking the turbine blad fru- 410s( qopn:rehees. 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 co j8h tax*/2a0,rbsjy .y vg-rlaster with a circular 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’thay xlag,*/bj8yvs .- 2trr0j 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 into ;ubwjuhde7,;y n*g,y work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=1000kJ) ,y7yb;n*ge w;dujhu,    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- l- cyn/d(ya:1j wfyc.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 bathw hgh nnxf(mce1;k1k2f .m44b room scale, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if ;xmknf f2bh 4k ne.(1cw41 hgmyou jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs mkbkhc522pro9:e 1qs a rope, and swings out over a lake (Fig. 6–45rekk1 qso:m5h 29cb p2). He releases the rope when his velocity is zero.
(a) What is the angle when he releases the rope?    ${}^{\circ }$
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distancepwm,hm y 4wgy7qb c6,0 of 5.0 m in 9.0 s. What minimum power output was used th4qwc,by6mp7mg0 ,wyo accomplish this feat?    W

  Some electric-power compahm8*jidn8p z -sj r+0xnies use water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 12hp8z0ixd 8m r- j+*njs0-MW ($120\times {10}^6$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 cafxhvjc*-g*5 ut in half. What is the spring stiffness constant for each of the two resultij- *vhcxf*5 agng springs?   k