In what ways is the word “work” as used iw-+:qh sj mh6xn everyday language the same as that defined inmjx+hs6-wq: h physics? In what ways is it different? Give examples of both.

Can a centripetal forcegzser 6.u i: :klw7qcl lj(**b ever do work on an object? Explain.

Can the normal force on an object a972b ,+drde7hm bz)a gz9wyftre, t+ever do work? Explain.

A woman swimming upstream is not moving with respect to the shore. Is she do,tyfxq3 gu03ping any work? If she stops swimming and merelug3 3,t0ypq fxy floats, is work done on her?

Is the work done by kinetic frictidv6fhlo *9iq .on forces always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out 9 dhifl qo.6v*from under them.]

Why is it tiring to push hard against a s(gi mz dz;*3b1skc ke khc-m fiu)kf538v; 7veolid wall even though you are doing no wu*if3 vs zebk)5 1 ezk;k83cm(f7- i;mh ckgdvork?

You have two springs that are identical except thajsi. f716 w,ev 81mk g9(yjny(zukbgat spring l is stiffer than springkj (9yz ,k7gg f8n1bemw.syja i6v(1u 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal forcx3km )e2 rqj.ie 51kl;zc ho+nhs8+sxe on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts fro z)8 rhs1lx +;2 kes5njqxmehkc+i. 3om rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your grav r8)dzxs9lj acd35lao58i . vbitational potential energy change when you.5d xjr8zsov53cdal a8l 9)bi jump as high as you can?

In Fig. 6–31, water balloons are tossed from the rb3 c/ *eoeitxv.wu 25 tr.w7jcoof of a building, all with thee./uwovcr25t.e 3wcj7 *xtb i same speed but with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowesm*r** l ma.wp hfsc:.kt point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/ .*ahcrm*.f kpsl wm:*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 u6dql8lu9 qy3 -wastu( pright on a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using tq -9(a8ylwld 63u qstuhe law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wim h/mitn n,7ic x6: 8+yg6sjetre (Fig. 6–33). The instructor pulls the ball back and stands agains 7t:gn86jeix+s6y,ihm/ nm tct 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 gravitational potential energy when water 3sj(6h5s hmtl at the top of a waterfall falls to the pos j 3(lh5mhs6tol below?

Describe the energy transformations when an,cf6gl00m,r db0sx a child hops around on a pogo stick.

Describe the energy / njgy an6cmair v,*sz95 .r8atransformations that take place when a skier starts skiing down a hill, but after a time is brought z.yca /* in9m5jvrsr,6ang a8 to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest g95f sj+ v,wd9 ay6cjz9j ixmbd*-qv0at 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 i9j5 * cvzmgv, 9j9bj+ dwfaxq6id0y- scy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen ll-toc* 18f0tw ukbn/g og in their path rather than stepping on top and jumping down on the othecuwgo8/kttblf 01- n* r side. Explain.

Two identical arrows, one with twice t;1e2 a apx1e jb*sm vd,l2sok;he speed of the other, are fired into a bale of hay. Assuming the hay2em,;p*1jk aodvssea 1;lx b2 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 swinging pn* qgd4+yysq8 tn hppwje9n- 2,ar-8uendulum in terms of energy, (a) ignorine8wnp42 rq nq9+tg *p,y8nh-ds -aujyg friction, and (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can itc3k 1p3uxh5 stcw pbe+9h7 m04i5cmqi rebound to a height greater than its original height? Ex3 eicqhm0wstbhmpc+34i k7pc5x 51 u9plain.

Suppose you lift a suitcase from the floor to a tabb oq n5ij-phay2 x.7*fle. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more- ibj 2ya*7 pxq5f.noh 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 power needed q o6wbt(0it 46r)pzbbrather than the work.

Why is it easier to climb a mountain via a zigzag trail than to ; x3dob+32qac13vy l hwhbz2yclimb straight up?zh c;2b hv2 x ydyw1q3aob33+l

Recall from Chapter 4, Example 4–14, that ye+f6oc- :ghd twzk,m)ou can use a pulley and ropes to decrease togkde- )tzmw6,+ hf:c he 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 concepts.

  How much work is done by the gravitational f5x53sw1ajxe e orce when a 265-kg pile driver fallsa5x wjs 51eex3 2.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work2tthvvl0 m -6s is re-mvtsvt0l6h2 quired?    J

  A 1300-N crate rests on the floor. How much work is required to move it ofe lklex)4qa 53 augwa7p/) .at constant speed (a) 4.0 m along the floor against a fr keo3 l)5x./u7 4wal)afqe gapiction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontall-bg*z4t7lm+ x 4u6kr kpph+zt y) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficientp 74mzt 4h-z6kugk tp++b l*rx of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by ap1wjhm97)j nb+)htsu force across a floor at a rate of for 7.0 s. Fi7)pj+wu hb1 )tsh9j nmnd the net work done on the box.   J

  Eight books, each 4.3 cm thick1 :) :3snxleo 8dhn08ugkthtx with mass 1.7 kg, lie flat on a table. How much work is requil0o8tnx:nx8h u3) 1dhgse t:kred to stack them one on top of another?    J

A lever such as that shown * ;.dkku 5j 8qh:qiiuvin Fig. 6-35 can be used to liff objects we might not otherwise be able to liff. Show that the :qkiu h8k5qidvj *;.uratio 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 mmyn f)iqvd y/w217vswet4 .o5 down a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36 nq5)v/2 17t .i4veyfmwy dows). 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 g.fgzmg9t)cawp o)mk33 -g jt+ ive a helicopter of mass M an acceleration of 0.10 gtam) w3j)gcmo t3-9.zpg fkg+ upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume the distance 05i ,vsl mcb2naxis 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 invqo74 owm.ze; Fig. 6–37. Determine the work done by this force to move the object w;v.oz74 meoq (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+mhmlg b1 j5zx8ph9 *g 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 o+h r5tex wcv)w0ws4w1xygen molecule, 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 i6o 8vyg0afc8t s 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 required to stop an electron ;7*k do ,pvmda$\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 traveling at 105ksv2 g-bo(y g:im/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts ad :i)hwr+uyk)4g+7 * j0 jskde1nniy xn average force of 110 N on the arrow o*xk) d+1gnwns ijd ryeu +y:i0k)47jhver 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 moves a fielder’s glove bacughrxc00t y5)kward 25 cm when the ball i0r)yxg uh5tc 0s caught. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its;:b /jgwp8ans minimum braking distance be increased, assuming all else is the same? Ignore the driver’s reaction tim p/gb:;8jw nsae.

  At an accident scene on a level road, investigators mea3q qmt2g6mox4sure 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 omq4 2tx6o3 qmgf 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 pitcvr:c :i x/+omzhed at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 mxi +/vzrmo:: c.    N

  How high will a 1.85-kg rock )nuu : 6rto0mjv5dl).u7y.f zgpe ,eago if thrown straight up by someone who does 80.0 J of work on it? Neglect air r u.lr)vte: 50uuyz.j7ge fn o6),md paesistance.    m

  A 285-kg load is lifted 22.eckxee5d wp:q9 kp.cm20h:d.0 m vertically with an acceleration by a single cable. Dxphmw 9 d: epkc2d:.cek05. eqetermine
(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 much must this kz*9 4hmvw 7jty-kg3mby/k kp3-r+ db spring be stretched to store 25 J of poj r3+mtb4 bh zkd3-m7v/- pkygk w*yk9tential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What ugt156 n9ytzy3is q7u is the change in potential energy9t7 nqsu51 tuz6i3ygy ?    J

  By how much does the gravitational potential energy of ap7zp7l,dnb k)ogwv9 ;wppz* 3 64-kg pole vaulter change if his center of mass rises about 4.0 m dur*zk obvw,ld9pp7)w; p nzg7 3ping the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h when it 7r- 6p*knmxhfstrikes a horizontal coiled spring and -k67hrmxpn *f is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book r5 kfez+5ics ep55gd37c mic:from the ground so it is 2.20 m above the ground. What is the potential energy of the book relatime:5zs+dcg k5ci75crf ep35 ive 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 a 3300-mx *re3 gzkh 2e1/7dh-bogzuo 1 z/oe11 b3 *h-2zxke dorghg7upeak.
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically next to a ruler. The end of the sprin:q q8hpgh)0gzgpe5 aromb,0 5g is next to the 15-cm mark on the ruler. If a 2.5-kg mpg :rbmzq h5e5ohg ,)00apg8qass 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 (5.37ijo+nb,y 5o mub 9nci6 06pii/9 mnzhm/s) and grabs a vine hanging vertically from a tall tree in the jungle. How h5970 , o9uiy6i 6/pb+biniom hj zmcnnigh can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slijo3 ;3k tjoijlyj2l9,gxv d65des down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a frictionlrvzldp nrg;vz( ba+4(4);x (oxl,p xless 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 cmq2gs i,n;8*k oa ;ittransformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran*i2i aqs,8n tcom;gk; 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 artiu+pje5xdrvb87k9l jgs8 +p+ d st jumps vertically upward from the top of a platform with ap ++j8 r597kgvbd+xuj ps8ld e 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 xtq litx v9:1 odc*f-(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 i*:dotv q1flx-tx 9c(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 thm5,zct 7 4g3tqwqix9he 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 what minimum height h must it b,chqg3qiz7m5tx9 4wt e released?    r

A block of mass m is at9k w-idpx ia00tached to the end of a spring (spring stiffness constant k), Fig. 6wxa i-k9d 00ip–40. The block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jh/ n(3 inglm j:+lo6oi4m9x fiumps from a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Ho6+/4igoh9(omm n:inj ixlf3 l oke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shfjxvn1o 50fr5 7wn2f/m; batbown in Fig. 6–41 is dragged up to point 1 where it is released from rest. Assuming n5omwj2 57v nbftf; fnx br1a/0o friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m//f.mkerioh9w q d37(qs 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 designiqn+f, 5p9/m9vfuz n, f;cf .yt kjwc)kng a spring 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 fjk k,v; z)fn9qwf5.y,pc/tcu+9f m nk 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 up1 v:apluvlx4 xy;z6zjhmy68 2 a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 95km/h in o3n- txjtev-e 5en :o/spposite directions, collide head-on and come to rest. How much thermal energy is produced in this o/3x-e nsj:ve 5tet -ncollision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slq ;e fvg)c ixp3xzj27e: 7t-dyide 3.5 m high and reaches the bottom with a speed oj-)x 3zpvy di72xfeqg c;et 7:f 2.2m/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from re75tx n,vyqusysy+r(vi9gel t3+r : x/st 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 trevkf7fctzcg1m ;,+ 1wle 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 bouncesnswdvc5(0/un ;a jh+w back to a height of 1.5 m sn5 wuhw/(avn;0c+dj.
(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 acro x+u8l x)tgdg0ss a floor with a constant horizontal force of 350 N. For the first 15 m the g0 )x+gldux8t floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed oyk4t gr3m(n b6sv8mb xwvfa62jzs 3*7f If the average force of friction is equal to one-fifth of its weight, with what speed will it reach poij( yz3g68s fb ar*w36nb724xmvk tvs mnt 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the fonp ar/g1.dn5.k2ef r zot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a ve. a(ji*sx j5q*,y:i msgmv*pery light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping a5s.*qp* xma,: (* jmg veiysijnd turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached tq) iviah.8upcz /h,k- yzy d8:o 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 beyond its equzy/:pid c kz)h qy u-8iav.h8,ilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glitm-rse5yh 1, ,kpx+ha der” (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 ah,1x+aky e,rpt-s h m5ir resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano tgf4z, ;siksr0 o a sixth-story window 16.0 m abovesrzfk,;0 ig4 s?    s

  If a car generates 18 hp when traveling at a steazecs;i93 ) peody 88km/h what must be the average force exerted on the car due to frictio zs9ipe;)oc 3en and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h0655uoz z3sbc2bc r :*uslwf n in 7.4 s. What is the average3:sb zobfn 5uu6r2zs05c*lcw power delivered by the engine?$\approx$    hp

  (a) Show that one British hobutl.95tj+sbzf8( s;h*rqb vrsepower$ \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 unitsq(a/(knly4;w erwsg/m , qv +h are often expressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 65km/h in about 6.0/ /mm5nl(w ffe s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constaml wf//5f(nment 75km/h.    hp

  How much work can a 3.0-hp motor do/+2 aibub6ggfl a.,( e p3erjx 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 motion9 :1yo ej(1bzuct ,prh takes 1.5 s, what average rt:o hju91,(yp zb1c epower was developed?$\approx$    W

  A pump is to lift 18cbe. fq2xew 0(.0 kg of water per minute through a height of 3.60 m. What oucex02(q.f ewb tput rating (watts) should the pump motor have?    W

  During a workout, the football players at State U. ran up the stadiu2wqv(yf ,go6 h-sau( gm stairs in 66 s. The stairs are 140 m long h a-so,(f(wvg6 q2u ygand 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 clibfb6lz s l (t-8bbwk;2mb 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 it cliuwz)pwz0sd3q7iujn-zpryzk:. / ;bqp2 tl ,5 mb at a constant speed of 75ky:pqn ik3,r z. 2wutdwsb)7j- p/5z0;pqlzzu m/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a mot9 xy- e:oyn7pqor have to be able to drag a 310-kg box along a level flo:pxq97n ye -oyor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts do-3tf3,pteyi uo x*wso4ddm +8 wn 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/hj vvtuet n adv9.tn 2(++zas-*) 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 defor*t-tvv aszva +.(e9+du 2n tjnms 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 remaihzia+7(wl xrtj.o1lu: 6t*guning 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 aver6jr(*auhx7ulot1 tgi wl :z. +age 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) i rrs/c9 n4dnd g3ugg-6n the 1936 Olympics shows that his center of mass rose 1.1 m from launch point dd-cgs g69g3ru4/nn r to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped track shown in F ni 7z6,b-wgqei2mx/t ig. 6–39 is to remain on the track at all timet6 w,-ximzqi /ne27bgs, 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 after4 zv einyux 0at,00ry1 jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass wa010a,e0ni4 zyvtu y xrs 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 fixed (F,6 nex7chf h 82inttl-odi7lo1a2a6k ig.7ol1n,6 e-dn khhx ia6olt7fat2 ci28 6–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountainz6 97 rvc v1-zf3gjowxgwyy48, ,wsuq. The climb is made in 5.0 h starting at an elevation of 2300 m. Calculateosj9 ,173yf z c8y6wwgg-w, 4qxzvrvu
(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 4u. rekp8yg5.gs uf4a elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can move 47,0-p:asob 3y4i9w 3rh rm00 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the power needed.i43p:wbrm9y s3ah r -o$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81 bm 6qcz (a-2ri wijt5.m before striking thr25jtia-(bq .cw m6 ize 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), th8 ueev). vag1xe 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 theav8 1 )xvuege. size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bwc 8+jj,m ,uf bnixy)s+fp94iar directly into work, how high could an 82-kg man climb a ladder if he were fueled by jp9 x+nuw,sbj)4cyfii+,f m8 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 firep/ 6(ap+gb3/dw l ebny dh:ef/d 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 sp9. ccbgij*:zl 3 1qavaring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of i1jcg3v*aa.qz9 cb l:1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over xp+b63xix*l0bg * e o*cc*qewa lake (Fig. 6–45). He releasesbxqce *0 io6g 3*w *clxx*pbe+ 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 h7dxjv8 m*usgf1k+1t vertical distance of 5.0 m in 9.0 s. What minimum power output was used to acu8m+1f7vxs d*kjt1g hcomplish this feat?    W

  Some electric-power companies use water to storal5+ gx-nz+3 i tu3cvje energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store thu a5v-x3 +t+ilj3nzgce 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 vz ne 4rl4lw)td)g3)y cut in half. What is the spring stiffness constant for each of the two resultil4n etg4 3vwr)zdyl))ng springs?   k

  A 6.0-kg block is pushed 8.0 m 0myf v *52zu:ew 9y)v1iyg etwup 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, how long wi tz.w1c.o5jlill it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losse1jzt.coil w.5s.    s

  In a common test for cardiac function (the “stress test”), the patient walksu z2tmiy+ r5cdu/ uy8lmb7m s; +f oq5g)ee7-w on an incli8/eq5 uyw rg2bsf7zoi cy-l++)m ;dmm5 7 etuuned treadmill (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 ockn4hn ik3j5 vfm(8d8f 500 m, what was its velocity when it left the v85 mdkn3kf i8c4h(vnj olcano? $\approx$    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 mvnt3e2 41/ eg,xtyt vrate of 95kg/s (a) If this watv1vgx2meyte,tn t 34/ er wheel is set up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s