In what ways is the word “work” as us - ,vpoo:dol0sed in everyday language the same as that defined in physics? In what ways is it dio0 d- p,:olosvfferent? Give examples of both.

Can a centripetal force ever do work on an objectdh w/lcp0duk e lv;vvr*4e/1 +? Explain.

Can the normal force on an object ever do work? Explaiu u h62skc.z2vxd,8h86meudu n.

A woman swimming upstream is not moving with respect to the shj.*9iirefis .ore. Is she doing any work? If she stops swimming and merely floats, is worke ii9r sjif*.. done on her?

Is the work done by kinetic friction forces alway3pfec;cgo5 -k6v 3f:x 8jhtrws negative? [Hint: Consider what happens to the dishes when xrte6c;v3f5 co w8khjfp:-3g you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you are doing no l2gxay7sj*3c wox72csl *gjay 3rk?

You have two springs that are identical except that sprd kxfus33f y),ing l is stiffer than spring33su ffydkx,) 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 on a block that is free to slid3x f-mz9i.mt de on a frictionles9-dx zf ti3.mms surface (Fig.6-30). The block starts from 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 gravitational potentialb;( e2f6*1fli /l h.biavrlit energy change when you jump lhi(i*l1 b e tri;b2a f/v.lf6as high as you can?

In Fig. 6–31, water balloons -m x3l+p za.mlare tossed from the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impact? Ignore air resis+xplz-lm a 3.mtance.

A pendulum is launched from a point that*hiqs6mmn 3 k*(gh3za is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Whic3i(* *qmg sn6m 3kahzhh launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rek si4 m90iiw0y wq,; -jlrz7pux psi7.sts upright on a table. If you compress the spring by pressing down with your hand and then rel 0pksyql 0;7xri 4.jsziw-wmup,9 ii7ease it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung fr. zk/cx4ge w*u(6kd/ *ez*oob ay15wl4okci yom the ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushz4blcy4g*y *d/k(k *iwe oec5z. 6ox kwaou/ 1ing it. Why?

What happens to the gf83)xeoki2e n ravitational potential energy when water at the top of a waterfall falls tonf3xi28 )ee ko the pool below?

Describe the energy transformations when a child 27( vqwyuve9d7a bv(w hops around on a pogo stick.

Describe the energy transformations th.+u x :3v3m j0nvwous 7a2etbrat take place when a skier starts skiing down a hill, but after a time is brought to rest byoa :n0u7 tm3erj3u x+wvbv2s. striking a snowdrift.

A child on a sled (total mass m) starts from rest as 0adz-h p-5.a kae o.:at8uqst the top of a hill of height :p.-8qaa a.o-sau st5ezh k0 dh 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 snow)?

Seasoned hikers prefer to step over a fallen log in their path ratphp6wg/g 0)*ulh1ptt5sj) e 3 nlke2ud mqs9 +her than stepping on top and jumping down on the other side. Explals0pu9 t) keh g5u6wm)tjhqgd3 l2+ne/pps1* in.

Two identical arrows, one with twiccb,wnw; jw f+6e the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force o+;6fnj c,bwww n the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simplgj8b2vae/0q,j:nzq 6x* nkude swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfatherzxnqq d vj0be n:2j6,k*u/8ag clock has to be wound up.

When a “superball” is dropped, can it rebound tl a9jy)q(;a1usyucra 0iq z0)o a height greater than its original;rcil )zqj s 0yuqy ua)10(a9a height? Explain.

Suppose you lift a suitcase from the floor to a table. The work you d e u brzkbs-m-spxond2 /-9f8;o on the suitcase depends on which of the following: (a) whether you lift it straight up or along a m-n9;-2b -rxu fpo8m/sbdzskeore 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 rather thatkm* jjoa )33yswqh 6d.iksik0,(*2 q mbv(zan the work.

Why is it easier to climb a mountain via a zigzag traillly9x;ozx 40bd0tc xzs9e4 a( than to climb straight u y z(otc;0 9x4az0l9dblx4sexp?

Recall from Chapter 4, Examplezqy* s7a ;ybo. 4–14, that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Accou*. by;qyzao7snt for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg 9 w2,df 3a.wdaga,y:b haiufvw):fh-pile driver falls 2.80 m? w g:b.9uy,)h d3 -w,a vfa2hwf: dfiaa   J

  A 65.0-kg firefighter climbs a flightlur9 .c++*ujw 3btcjwh/ j( 2) oobqdb of stairs 20.0 m high. How much work is re9+q )c/(b*j3tjludwoc hw+rb o.ub j2 quired?    J

  A 1300-N crate rests on the floor. How much work is v/- iruod1,8dqgd 0 ey/*x8povb obf 4required to move it at constant speed (a) 4.0 ig0d y/qxoo-e p dvb buo,df48*8v /r1m along 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 crate 10.3 /. p. ci5/ogt ybz g2oq(.xaemm across a rough floor without a/co o. zb2xi.gag5y(p.me/q tcceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across aq9;u7hk ;ovb hrj)w( f floor at a rate of for 7.0 s. Find the netob( j) ;h7f vuhqkw9r; work done on the box.   J

  Eight books, each 4.3 cm thick wi/ 1hj/ky svcg6th mass 1.7 kg, lie flat on a table. How much work is required to sta1vkhjc / s6y/gck them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects we,nvykaj/iup8zj :.k4a4 9jtuea * a0b might not ot kytpiuuveb4j*k0j.a:a/ 489 azn a,jherwise be able to liff. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kept from accelnsc6 1t/ rnd2a(mev9 f56t vteerating by a mt(2cera196 e65/dv t nsf vtnman who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter of mass M an accelfb )suk: -wekfa,8c3 )m aedo9eration of 0.109wbu f k83e,:-a))scekd mafo 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} $ 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 7o.t*-k mr6fqhk)i ga 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 shownsswn,t b+x -vyw4b *go;awg77 in Fig. 6–37. Determine the work done by this force to move the object (ab-vws sgw;7+w4g7,b*yt axn o) 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 pag455e,hvvhl( kh bw 0j:eom:wrticle 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, witndc;4ablaswd q+0z,8 h mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor ha ;l.xdyw.v(nq5 zbp/1ioi (ves its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required tojc lb7/nq 2wr0 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 guk,zqb s.zx6 *r0 i:n1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bowi8yq*4 ik(fixckj5 5cj/wd 2u whose string 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 (4 */ixcf2j8cdw i ukqky55ji leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder0sf vn xf498br’s glove backward 25 cm when the ball is caught. What was the average force exerted by the ball on the glovsbvx n8fr0 49fe?    N

If the speed of a car is increased by 50%, by what factor will its minimum bra04srsm 2.my,x(p/fxoc fozc 5 king distance be ic (myf . /scofxxpo 25zs04,rmncreased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road,ys( gh:1m j;lf investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use 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:g;fsl (jhy 1m?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the t:4gmfose vt(n,m p a84 ;l9oeuime it reaches the plate, it may have slowed by 10%. Negleca s4vogn9fe8l,4;omu (te m p:ting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if4a( a/)l6bnankyj: wo thrown straight up by someone who does 80.0 J of worlya4wo)n6 j(b/na:ak k on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleratiyw i,5 /ni lmitfxc2w011rqt7 on by a single cable. Deny f2txi10r7, l 5miwitqw1/ ctermine
(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,dpn 43kg)a* s:al: bm6ktqj .y k, of 440N/m How much must this spring be stretched to store 25 J of potential energy? qkm k nt:d*ygl.6:3 4sja)apb    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What i1fe z4iez+x yft-z/5i s the change inzzy tif4e-zf5 +x1 ie/ potential energy?    J

  By how much does the gravitation2+-9zl pcc ar b)uk8zhal potential energy of a 64-kg pole vaulter change if his center of mass zua) k89l+ c2 cpb-zrhrises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface hf vdzq.uk*) 1mgb;vc3(jx lisvy5n , .m3a. wwas speed v = 65 km/h when it strikes a horizontal coiled spring and is br.k,m.x 5nc vybzwd; aiw (g1j*3qlv) sf.mvu3ought 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 from the ground sl1xnzv2( vh2eo it is 2.20 m above the ground. Whateh2 z(vx2 vnl1 is the potential energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and climbs to the top of a 3300-461 9veqr+ozf ned1 vlm+v eqr61zfole 9v4n 1d peak.
(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 3y5fgsk1iv w4py t) c2a6-hn vend of the spring is next to the 15-5s k hv3vi )2tycywngp f1-4a6cm 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 ruler marks?    cm

  Jane, looking for Tarzanlv (81amto9b +jz(v qu, is running at top speed (5.3m/s) and grabs a vine hanginba(ztj quvv om98+(1lg vertically from a tall tree in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frictionless 7h7hh: ns:pet 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 shov -,a ymuqh-g a7k8vd0ge up 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 5op+u j2dhwtwgkcv/lwp- +8 8gravitational potential energy without the aid of wvgj2 tc dwo8w+kl uh/-8pp5+ a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertica,s b+a nu9pd.ry*4l pklly upward from the top of a platform with a spe +sady4 pk9,u.*n plrbed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose spring stiffness constantts7zu:.dx qw) is 950N/m is attached to a table and is compressed down 0.150t)dw 7ux.qz:s 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 track shown in Fig.somtu 2 (.h1f lc57vxkmd 7g:q 6–39. If the blockmq(mg7 xouks7 tfv. 5 d2h:l1c is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffness(iwhwrnk1p1n j/b+ va 8tj+ m8 constant k), Fig. 6–40. The bloc8kv18bpw/hnn1(r+mw+ t jija k 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 bridgedxx m0x u8jih:valh y 1r,(+p:. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m.jhx:ymxh0 r: 1x,l( p8ivd+ ua (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 t/gr.tsuv 4/+ mzc/p yjo point 1 where it is released from rest. Assuming no frigrtuzm./s /pcv+ /yj 4ction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at anbd, y 2b-xubo-j a+o;o angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at thhl/xk ju ) -vug3qc.yi418aete bottom of an elevator shaft. If the elevate-lj k/xig3 )4t v.qay 81hucuor 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 passengers.

  A cyclist intends to cycle up a 7.8/7mk;yr1 cvh zr8n (oe $^{\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 3j )jl9-8qvs;3rh jhzb)htg ,;amnc oy 23gtfof mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy vlh3j 3h hf ;tj)9g8)jzqn- arc,2 ;mgboyts3is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m highqzub 8nj ;df0vx-5;xm6e4pjz and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generated in ;v468exzb mzd5 0ufxqpjn j- ;this process?    J

  A ski starts from rest and slides h(6d6 nu -whb )v64*btpk5h6 (tbjsnywd,vf fdown 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 jebk t:a 2(;rsfrom a tree 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 heighr h o-f(ukb7o:t of 2.0 m, and it bounces back to a height of 1.5 m.k:r 7hu f-b(oo
(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 with a constant hwc8m3rxt8r thp /t5g*orizontal force of 350 N. Fo c*8mgwh p8t3rtrx5/tr the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6 - ab98pxn is2buq5(dz–41 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 mb92a8(p-d 5nxs uibzq. $\approx$    m/s

  A skier traveling 12m/s reaches the xr xat)d ox.s j5khui6.;+jtv-,zp q*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 attached to a very light horizontal spriog :pnj2gb5p wi89 dm7ng (k=180N/m) as shown in Fig. 6–40. It is npg:wi957g bo82mpjn doted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizi+-n -u;kot ,hle36 wlfya w3pontal 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 po,op w-uln 6 t3;w-a+fhky3ielsition, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” vzf9 . + i+rk:h*demcq .:cpgk(mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 mv:z9cm*r.qdk: .ecfhkgi + +p. The glider eventually landed at a speed of 200km/h (a) What would its 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 3ca; :ool0k so5yj1uw a 315-kg piano to a sixth-story windows0o 1ju53: ocaoyl ;kw 16.0 m above?    s

  If a car generates 18/ u6hd7ci+ 9 :ahmw (tmb/zw.9trwxjd hp when traveling at a steady 88km/h what must be the average force exerted on the carw .7/9tjdzu(rambw6h +cd himxw t:/9 due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is the averar; 0kya7i iu *ajk7r*cge 7k;0 ai7ir kyurajc **power delivered by the engine?$\approx$    hp

  (a) Show that one Briti(n(ft-o,w4 e7yxpq.oj tm /nzsh horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressemsubi 4xv 25 eq-;rg2pybm03td 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 6.0rb3nv+h0i5os4km )jx s on the level when it is in nksjb i04 +n5hov)3mrx eutral. 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 motor dee:v 4 +9xsnb+qqs1b co 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 takesc8jmu lk0xhv f* uw48+ 1.5 s, what average powem4 lu+f8ck 8xh0wju v*r was developed?$\approx$    W

  A pump is to lift 18.0 kg of waterazk 1rf8/z)4v v1 vigf per minute through a height of 3.60 m. What output rating (watts) should the ffv 1zzka4 r1vv8g)/ipump motor have?    W

  During a workout, the football pl2. ;v 12d llmqvraxq3aayers at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclin3qx;v alarm1vlqd 2 2.ed 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 climb a 6xa-pvh*4oxd ;t s j;iwc b696o.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 h, h;pn nmzw4xjpgg/:2p. How steep a hill can it climb at a constant speed of 75kpxnhp:/n,gw ;2 4zgmj m/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have tx,((wa .v jzvto be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficiexw.a ,(v z(tvjnt of friction is 0.45?    hp

  A bicyclist coasts down s9ud5x urbqg :n rbhr3ll)+v/;ddh0 /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 hat 5cpmq*l3h: vve built “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness co*35 plcqv:htm nstant 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 remaier omz;-su; o:-f as*vning four shelves are each spaced 30.0 cm above the previous one. If the average boo;-o* zm;res vafou s-:k 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 are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long j gu+pq3pp;8(qpgg u4 mump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What mg 8p;pg gpuq3u4+pq( 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 loopedzrrgu:hb+qn2m69nt 4 p3) lsc track shown in Fig. 6–39 is to remain on the track at all timgsq b+42l:n3hc96m )przr nutes, 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 4cw)+mq.cyu f5w qn18 gzurtq0)/ixc 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 was 78 kg and his terminal velocity was 3g+ ycq w/q z)5cu8nt1wi)4rfm0uqx.c5m/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 othe gn:6+6f+xcm 7sa bjdbv .;;kpwqrl ,nr end is fixed (Fig. xknrwb 7. b6d6ql ;+,n:amgj sp+f ;cv6–43).
(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 mountaigua jm l78e(ywq:lmre70dy6*n. The climb is made in 5.0 h startie8e:q(mywmdlg7a0r l6*y7 j ung 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 bres3((hdef tljp7)z av5aks when a 920-kg 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 *ck05b,wwmjls 5x s4b claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 5j5 cxb b,4 m0wwss*klm (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a daml)+p/r 1e ub/+xq7 dkxbx z/xs at the rate of 650kg/s and falls vertically 81 m before striking the turbine blades. Calculxd/x/krq sxzb7+lepu 1)+x/b ate
(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 vertical5l: vqzk ttk gb;o*o:0a).p mrb:2 j*fbipin7 loop (Fig. 6–44), the difference in yo:p f)n2a*ztobp0 jmlb:k:rog 7 t.k i5;biqv*ur apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly in vy)k,,v g1zqft)-asy to work, how high cou1 g)v vytq,-ys,akzf )ld an 82-kg man climb a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is firex c;q hxcq52;hb u5b)mom2 e;md 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 six yd)ys li;ml2;8)rc .axs/ kcale, the spring inside the scale compresses 0.60 mm, and it telyy; s)2xxaim lr)k/ ;.lcisd 8ls you your weight is 710 N. Now if you 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 a rox9xxitt;j;y - i52/ehxl* kgape, and swings out over a lake (Fig. 6–45). He releases the rope ax 59lxe;th*t-kxj;igx/y2i 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 athlety9dhj (y j2 lz;9sm07l ekhfc,e climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output jm09;h h2 jzldy ,kyf(ce 97slwas used to accomplish this feat?    W

  Some electric-power companies use water to store zjk0v -mrsv .8energy. Water is pumped by reversible turbine pumps from a low to a high resejs8k -0vvz r.mrvoir. 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 7a(4-ni 1 vaxywwu xbh75c*tt is cut in half. What is the spring stiffness *v4ui7y 5xw1xc tbn hwa7t-(aconstant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m0 8ql0qtg tq:f i.a57yxt-qlu up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can acceleratetk*3gk)+ oqrzfxv:3 bn l8t,ocj- vkb ,ohd/ / from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the pbx dk 3 objg-/v t/, kto+3lnhok :r)*,czfq8vower stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient walks on j eu 63r8gdv5kan inclined treadmill (Fig. 6–46). Estimate the power re5jr3eg d6uv 8kquired 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 c mfs) pv37zrfsklrk 0; 9l2gbv tu2n9qm1m 2,a 500-kg rock vertically upward a distance of 500 m, what was its velocity whevs gm 0,p 2lk9nm1t;fu7qmfcr )2k3v9 b2 lsrzn it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 3kmrj-e3h.k/bh l ajtjf u:/. 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, whu/f/ ml j-k.har3b e 3tjj.kh:at is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s