In what ways is the wod fm8f9j.c6l6b q -nxxrd “work” as used in everyday language the same as that defined in physics? In what ways is it di d-x8mf6c6bjfxnl 9 q.fferent? Give examples of both.

Can a centripetal force ever do work obylqh:5-lp , my8l vt0.4ri mwn an object? Explain.

Can the normal force on an object ever do work? Egyre xv++p1 6xxplain.

A woman swimming upstream is not moving with respect toag d7vj9o ,f4drio*s/j:hrw ve8 yzy,b/ b-f) the shore. Is she doing any work? If she stops swimming and-y:9bjdo,*zjw 8a) fv /4es7oh/g rf,virbdy merely floats, is work done on her?

Is the work done by kinetic friction forces a hk wo5ijzgpr 8t5dy6y- (k1j-lways negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out from under t-p-tw jy 5ohzgdir5( y jkk861hem.]

Why is it tiring to push hard against a solid wall ea(+ 2/ 0;p+smq bqlg vcc9ahljven though you are doing no wolg29qabsq(0p+/a;l jh+vccm rk?

You have two springs that are identical except that spring l is stiffer than svgg- (08 pln.nwdsluq (u 3ze4prin0nugl g 3ev84lpn(us(w. d-z qg 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force o.3;j; u mvl jjjip;nm )e3yy.gqn(7pf n a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint ; (j 3nf7nmpijm).qeyp ;yug vjl;j3.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 muchultw7 j 2p2cq6 pux;:g does your gravitational potential energy change when you jump as high asuu6p;c:tj l pg2x27 wq you can?

In Fig. 6–31, water balloons are tossed frog-k:f8jm mga +y17crq m the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on i:mfmgr7 a+1y k gcj-8qmpact? Ignore air resistance.

A pendulum is launched from a point that is a height h absy ygsxk+e 4k,js e,bhi;k,,3 ove 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 seconds ik jgh,3;xeb+,,eskky4, ys 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 thefnwl,* xq 8p ns4tmv6) spring by pressing down w8n fqm)nwxpt ,sv6l*4ith your hand and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hungn5a q/wm8gs 3gc; :;rnsv0 msl from the ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall s 3 m; /n:ngsc0 r;5wmgvqsa8lwith 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 at tzx e8l,n6+n j3rkp8 fq+hzr a2he top of a waterfall falls to thalz,hqrx 68fp 3 n28+erzkj +ne pool below?

Describe the energy transformati t*z kscjc049fons when a child hops around on a pogo stick.

Describe the energy transformations thatbm (zuk: -j:vh take place when a skier starts skiing down a hillbz(mk -uh::vj, but after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest 4 mec2h7lpzje7gphvdu9/*q5 /,wz atat the top of a hill of height h and slides down. Does the velocity at the bottom depend on th5a,zv7z*cph me jl/ gpteu9/d2h wq74 e angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefe./o6 rsx nnvg;r to step over a fallen log in their path rather than stepping on top and jumping dno ;g6 /.vsxrnown on the other side. Explain.

Two identical arrows, one with twice the spe5w53mnx ;6b f ;wwv2mbhba6wsed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow willw5h wnw m56sabfvx3 ;6wb;2bm penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of 7a x00zkz6y0c 5wmhdoenergy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has to b z7m500 dwk 06axychzoe wound up.

When a “superball” is dropped, can it rebound to v hbq)6b ,pnt+ bejm(kp1u v9g89 pnx2a height greater than its original height? h pvgb 9nkqumje)+ tn 289(pb,p61 bvxExplain.

Suppose you lift a suitcase fr0mx.j2lvzss0dic l;p* 0ar 8nom the floor to 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, as x*8di.0r02zla;jm0 vpsln cnd (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than t g55 9q*rouxps+j rzokq n) dthxe:c57j e-e*4he work.

Why is it easier to cl229nu4ebi lwy1q2+h syv* xupa;tb( nimb a mountain via a zigzag trail than to climb straight up2ln yatvw* 2h;+2eisqu y(9xpbu 4b1n?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes to p b:jo7p- er:cdecrease the force needed to raise a heavy load (s c-b :ej7oprp:ee Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pile driver f 4r;f0q lyl8tuh)9jc malls 2.8hl8l 0 9tqcu;)y mrj4f0 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. Hotbyh p95bqn 57w much work is requihtq5 795bpyn bred?    J

  A 1300-N crate rests atjy990i,mh 6zib5 t l9j3c2p0lo anu on the floor. How much work is required to move it at constant speed (a) 4.0 m al0l u5licm9zoi,23 0p9aybhn tjjta9 6ong the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg.owm0ql2rel2 crate 10.3 m across a rouqml we2ro.2 l0gh floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accexd s2j2+nlh8ft(knzdo g(:8dlerated by a force across a floor at a rate of for 7.0 s. Find the net work dg o+:nft2h2(xdzk8jnld( 8 s done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table(mawwm/ l) 86m*avryi. How much work is required to stack them one on top of another6riv()my *m8am /wwal?    J

A lever such as that shown in Fig. 6-35 can be used to liff otsc*s+ tj *rf:lgb3p7bjects we might not otherwise be able to liff. Show that the ratio of output force,l tjt:gp+ * cr3f*7sbs $F_{\mathrm{O}}$, 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 ke t1cx5uf8kjn7*l.pk 1l jomo0pt from accelerating by a man who is pushinc 08 uojp1k .x flnkl*715otmjg 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 h0uiyilhhrw8yt9:owlw 16e8csdj0gz : +6f6 m elicopter of mass M an acceleration of 0.10 g upwaoi8 we9itd6: 1hwj+y 8u g czll06s0:rmwh 6fyrd.    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 gn )-b+ )gig5vyofdu g ju:l,+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 aleot8c ;2bh*th fwb dn1s i--w:ong the x axis, varies as shown in Fig. 6–37. Determine the work d:-w2-*hbto1 b8ts;ned ifw hcone by this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

  A spring has $k=88$ N/m. Use a graph to determine the work needed to stretch it from $x=3.8$ cm to
$x=5.8$cm, where $x$ is the displacement from its unstretched length    J

  The net force exerted on a particlnyziy+0 ggns23 b t50be 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 molecule, with jqd * pj(r axxp8ye.x ;o5k5n1mass 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 speed increased?py 6m.kk;o4 zw $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is requirereg +)5yzd3:d wuo dc :ovlu*3d to stop an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar tr:en2f/j(l uf l:4bb yjaveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose stri / n8hff;oty bvwi)4.rez-9k mvo/ :ypng exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves the b/ o.:io4wfnbk)vm ypy-evt/ zf9;r8how?    m/s

  A baseball (m=140kg) traveling 32m/s moves a ffizw60kyrl7; prt wj hh59b7, ielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the ball on the glww0ilyb,j tf 9h7rz5;6kp r7h ove?    N

If the speed of a car iq0*wcsn 9;w wes increased by 50%, by what factor will its minimum braking distance be increas0cs;nw* w9qewed, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, ih0;r +4tz-q e6spkguy nvestigators measure a car’s skid mark to be 88 m lt4hk +0p;g eq-s6 zryuong. 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 the car’s mass not matter?)    m/s

  A softball having a mass of 0.21-*t fkb hp3dp5 kg is pitched 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 betk1d *fhp3ptb -ween the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if throfqxu4b*z4m,* 8faw sia7l tb-wn straight up by someone who does 80.0 J of work on it? Nta fl7x aub* 4wq,b m-i8zsf*4eglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an accelera(n)t tili/ztj51 *yj3 c rqf.otion by a single cable. Deter i rt3tz.oj/j)i*yt l1qc5f( nmine
(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 440kez1qtkhl7 yn h(s:oq)yy,8d 1odo)+ N/m How much must this spring be stretched to store 25 J of potent lntso ) q kqkd,dzyo1 (7oy):y+h1he8ial energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m highusg.u3 co:6+d ba 0b.j-f2 uk7wchtxler. What is the change in po+-7uwluj2koc :xhb3s ga.6b.tdf 0cutential energy?    J

  By how much does the;zx/mbp37w l r8lwiq8 gravitational potential energy of a 64-kg pole vaulter change if his center of mass wb xlz;p 7ql8rw3/8mirises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h whet . xrovdm1,x(tk(j53woem o;n it strikes a horizontal coiled spring and is brought to ((;x 1w.t3toem oxv,5jrmd okrest 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 bl5nzr1hws(r6 ook from the ground so it is 2.20 m above the ground. What is the potential en6whzs5rl1r( nergy 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 olg2.5up( bgne vl/* l)md6vcto the top of a 3300-m n.p g/lbe5*v v l cu2)dlgo(6mpeak.
(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 or/-w ;ety x)hvf the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ru x;tew)r-vyh/ ler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a vine4fnn4 )ufv sz7 hanging vertically from a tall tr7)4fnusfz n4 vee in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frictionsm);* nubsp i4less 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 frictionlip9fr (2dbj) dess 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 eqm.fl z o09li5qme8n6ssp u9 2nergy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran l0s5s6qpq lu m8e l9m92of.zineave 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 oq8 ajsbq.(xg8f a platform with a speed of 5.0q8a(sg.8qjbx m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose spring stiffness covmj2obabk(r +dm 45*p nstant is 950N/m is attached to a table a2 obmm rdvj4p+(k 5*band is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the looped trs5 /ium3vx gp+ack shown in Fig. 6–39. If the block is to remain on the track, even at the top of tg5/vx+ p i3umshe circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is ajcf554j, tsxuu6:wyc . 1zvq/jx a: gittached to the end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial dis5fxv4jj :i .,y wcq1 jgauzcu:5s6t/xplacement $x_0$ 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 jump ;odoed*9pn+ g k,arx8s from a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 318axo rp;k no,de*+d9g 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 dragged up to poioxm75 j:pmqe g1hh(;z qq4tm*nt 1 where it is released from rest. Assuming no friction, calculate the speed at poiehmhoqg m(;tzq1m :j*q45 x p7nts
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown withbrm v-exe+. f(i4ff- x a speed of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designingd p3 grz6ba*+-:ov mda 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 spa a o+-g:vdp3*d6mrzbring 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 cycl 82gi*vpnnbc2e up 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 o5z1jk xxi*e8b *b- bwin opposite directions, collide head-on and come t8o*ik ew xjzb-bx51* bo 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 z6*58 zgw)k(r ckkuwqlfxb -6the bottom with a speed of 2.2m/s How mul5 ) zkk6u 6(g-x*kwq8frcbz wch thermal energy due to friction was generated in this process?    J

  A ski starts from rest an+o ( dyyi1yb)md slides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m above the grjqob 26z hjqs 0;y5gt9ound.
(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 of7guyxx*k3 vkd 5dm f unq1+5t1 2.0 m, and it bounces back to a height of 1.5 m.+x7u m5 k5t1ndxy kv3dqufg1*
(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 )y+hdi i d;2aswith a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient );i s2ad +yhidof 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 speed3phy ks19dbc9 of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distanc3bh yk1d99s pce traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches th2(dv bre4;x czp (lfx+mdm,)se 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 fj;m .djmsns-(irmly attached 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 stopping and turning back. What is the (msjj-smnd. ; coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to asi7qsq.;.gwo0tp * f 9ghsy,i very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of frictq,g*. g.hy; 0 sptos if97wqsiion is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shutte k,220kq8h im -twmbvuhza6 9le used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landihka2mt wb q0i82e- uvmh 9z,k6ng 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 ,c b5hkdzi6aujbq; :pe r9g75315-kg piano to a sixth-story windor6 c ,;beqi9:hza5p ku57gbdjw 16.0 m above?    s

  If a car generates 18 hp when traveling at a ste+)7xg b2 gid(sr7o g zog+0uqoady 88km/h what must be the average force exerted on the car due to fr (idb)qo0+s2o77gg zgx gru+oiction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95 7nlatw i8il64ef*c3m km/h in 7.4 s. What is the average power delivered by the ecn6 *8miw3l7ltaief 4ngine?$\approx$    hp

  (a) Show that one British horsepowe*)z kwun3c.bjiw)oc-r$ \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 formx-a-5ujh7kfk oj 3)h q1 nz-dj 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 thag h-0-d;4/nxiyp, jw+zwnx ret her 1150-kg car slows down from to 65km/h in about 6.0 s on the level when it is in igdwwy/n-xepx 0jr; -+4n,zh neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp ocuhy51 d91*evtpo f )motor 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 ta bs-pcjqi-ff4 49*kltkes 1.5 s, what average*fc9f-s -ij4 pt4qkbl power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water g 5qb lo)qk4d,0a6y gb;c9szstd.6vh per minute through a height of 3.60 m. What outpgqc hyb,oq5dkal 0sdbv9. tg 6z ;4s)6ut rating (watts) should the pump motor have?    W

  During a workout, the football players at State Ucp7i 2g/p5uzen to3z;d8rfj- . ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined at an angle tru/z8;gpofic3 5 ezd7 nj2p-of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb u5l 5b u2d:gs1tnbe zrt u9w. ovk-u57tk 6(tga 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 )e(+ta bkg : :zuvsq.- 9exwgdmaximum power output of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictionaa k9wxusg-tvd(z:)+ ebe:g.ql forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg bou bm (3+j1htgax along a level flh u +tg1(bma3joor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down aesvp idn1 *zj4*u1 pb-w8gva6 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/hia61eqmz wy bn0m d50v8-d fwh+6d v)y) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanentlyzv v 1yani6fdw0eh8-db 5wd06m +qm)y 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 rem6if c ,jvs xrcw)6euc04o+n5 uaining 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 ic4scn 6ufw,o5v 0jc+x )eu6rbooks 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 shdyo;ic) t6 tg2yr --gxows 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 laun) tgo-g-d;t6x ryci2y ch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m j0bq;9 s j/fpvj1 (kkt)(yvcq tj/ln7 sliding without friction along the looped track shown in Fig. 6–39 is to remain on the track at all tim t; jv1( 0j/ slq79yt)jj(pk/nqcfkvbes, 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 aircranq7+pmi6 -+aeu p 0 ypxf+.ny:pkyw 7yft without his parachute opening. He landed in a snowbank, creating a craternyy6 ppapey qwni+p7x ++k 0:f.myu7- 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 toxnav57g +q(vl u4 wd*80 szuzj a horizontal cord of length L whose other end is fixed (Fig. 6–43). va7 *qjxzuz4du g (5n 8lws+0v
(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 offmj384+n dyd tmx0d8: 9bbgf (7 wmvfo a 3700-m-high mountain. The climb is made in fbj8 4vdt(dd+7 3 0mb8oy x:gnw9fmmf5.0 h starting 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 elevalwpjb4,c..o ugj2n -h tor 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 Califorjzr9g)bd(i 1n nia claims that its lifts can move 47,000 people per hour. If the average lift carries peop1zib d9gn jr)(le about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at thi(9 k10gjiceg0*oe x+a q gwf7e rate of 650kg/s and falls vertically 81 m before striking the turbine gqwg79jko+ 10x gfca* 0i( ieeblades. 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 l9gn3w; g -sbq (cbzrh0q9l4ivertical 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 4cl(qbq wbzg9;-gihs90 3 nlr 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 into work, how hmu ,sb,)nvh,s-f rt *ligh could an 82-kg man climb a ladder if he wehsmnvl ,rs*, ,-tu fb)re fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward angljq:-hip;lo s3ka65m je 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 compresses 0.6d0,vj6/y l/(eh-8gl js 7qfh ocmf2ee0 mm, and it tells you your weight is 710 N. Now if you jump on the scale y-se6 h8ef,qgjc j(h7 m2l/v fle/0do 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 a rope, and swings out over a lake (Fig. 6–4c5kj s6 0yb1u ugrwh g818q8(,wbmhov5). He releases the rope when his velo1bowm 8g6qr( b8v,j cgh1uwyhu 85 s0kcity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5.0 m in 9.0 12l g.h(tkb4rly3maa s. What minimum power output was used to accomplihg 1l( alrab3m.ykt24sh this feat?    W

  Some electric-power comvznkihjmo+ xi4:..+n4u4c zopanies use water to store energy. Water is pumped by reversible turbine pumps from a low to a high reser jm z4oi4n: z+vocx4k.+hni.u voir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in half. Wm vt1ou3/6srmstjst2pr a,py h2r:;3 hat is the spring stiffness constant for each of the two resulting spr2r1pps3, ruo 3tmm : r/s y6;tvtajsh2ings?   k

  A 6.0-kg block is pushed 8.0 m up a roughlve/) o88ehb u8cqos;jio5l/ 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 35k)g zxurqjck;y29 z/) ym/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional loy9y; zx/)zcq) jrk2ugsses.    s

  In a common test for cardiac function (the6 56bmqvq d8wn “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the tq 6wd6 b5mnqv8readmill 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 ovz +w; x;tg6l w:2an;u 7lbela distance of 500 m, what was its velocity when it left the volcanou wonax;wl76;ezl:gbt; 2 +v l? $\approx$    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 nx.;c+)jq 5:jd ntoclmqo,y ) 2.0 m at a rate of 95kg/s (a) If this water wheel is set upcjy )cm, t+d lq.q5xono;: )nj 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