In what ways is the word “work” as .q9x* w;wbsms f-nhvtrvm0qy2 c/+*rused in everyday language the same as that defined in physics? In what ways is it different? Give exvwym9c w-.ht v* nf2+ 0qsqxs ;r*mr/bamples of both.

Can a centripetal force ever do work o/ mu.ai:4b01jyz)a ew b7uerdn an object? Explain.

Can the normal force on an object ever do wor6aij;1; j,n3gu sn/qyb :eboqk? Explain.

A woman swimming upstream is not moving withf,os d;5o 1ik* ycvzx3zsy2b) respect to the shore. Is she doing any work1fo)*dss byo2 v i;53cz,xzyk? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? :v1/ bqwv t)mweqzt*zj1/w1w[Hint: Consider what happens to the dishes when you pull v w*jw/1w)z 1v/tq b:teqwmz1a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you ho fj9ntwn x0w.9f 9;gare doing no wxw;99oftw . nh0jn g9fork?

You have two springs that are identical except that spring l is sti4g twscz;h/3lmai6 , fffer than sprw a4s zg6tcfihl ;m3,/ing 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 h/, bth*d-4s8:ssidqld ejx ;y orizontal force on a block that is free to slide on a frictionless surface (Fig.6-30). Tbs jy-4q s8dtd:,i hs*/d;elxhe 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 f:s ljq5o lu+4 6fguh-potential energy change when yoq-ol:jgsu 4 6h+f5ulfu jump as high as you can?

In Fig. 6–31, water balloons are tossed from the i o 6j;--lrysgroof of a building, all with the same s y-gjr o;l6s-ipeed but with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launchedncx1asxysopx ok1gr.sra,6u.v*o17 x h(l(, from a point that is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given a,xx 17c1 6r v ..pxar,1ysln*uooags(sx h(o kn 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. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress the sprin3 mmxiw)b9 mm:h :chx7g by pressing down with your hand a:i cxxw:b93m mhh7m)mnd then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The instru1/qgfx(.*cwrz5dqa* a qbgl*ki(nz6 ctor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release 5 / x*rflb(6*cqa.ig* ank dqzz(w1q gthe ball without pushing it. Why?

What happens to the gravitational potential energkei m)h;p ;:;- cvdzbjy when water at the top of a waterfall falls to the pool bjd-epv; ;m :z)bikh ;celow?

Describe the energy transfywsgmd eur-h 4w4u::q2vtt2+ormations when a child hops around on a pogo stick.

Describe the energy transformationibw/b9 q0p m(au5d9rzfcgd 64s that take place when a skier starts skiing down a hill, but after a time is brought to rest by striking a snowdriftb4u idg6cw(/aqm0 rp zfb 59d9.

A child on a sled (total mass m) starts from rest at the top r4rc0r g16sphof a hill of height h and slides down. Does the velocity at the bottom depend on the angle rp06hs r1c 4grof 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 rather than st5b+bap 0eslkomw64p /epping on top and o6p0la+ kse/wb4 mp5b jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the other, are fired birr91 2rdo/m5uvi t )r: /ulainto a bale of hay. Assuming the hay exerts a constant frictional fi r:bm)u9lair /u/v5ot r2d1 rorce on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy, qf. vip zq396i(a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock haiv.pqqi39 fz6 s to be wound up.

When a “superball” is dropp4plj t)49 f6f )j gjov9tdprd6ed, can it rebound to a height greater than its original height? Explain 6 j6po 4pfj f4t)lgd9v9dtrj).

Suppose you lift a suitcase from the floor to a table. The wohccxx, i()m 7drk 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 tcdc )h mix7x,(ime it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power neede0fu v1o6e se:fd rather than the work.

Why is it easier to climb a mountain via a zigzag trail thhlk-/ff4t v r m3g0 wna.kh6m,an to climb straight u./-fl4kgh k0t63w rnmmvfh, ap?

Recall from Chapter 4, Example 4–14, that you can use a pulley and r+(w) -sc :sdj9cfn p7+xsnksz-no;kkopes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for eves(:ndsnkscsox wpn)cj 79;f kz+-- k+ ry 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 26y w,g+(8blks2 ew(vv f5-kg pile driver falls 2kg vb+( 8 v2(fw,lywes.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. Hovc;t f;gx)w3uocbnx4uy l0q(x1 / c2zw much work is rexzog( b1;wxq)0clunvxcyuc /23 ;f4t quired?    J

  A 1300-N crate rests on th)gg 0nouo i xqt..lv: +xmyj*8oe31xbe floor. How much work is required to move it at constant speed (a) 4.0 m along the floor against a f:0lxtou .x y8.x* v3gqjogio1 +nm)beriction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the moverd4ad b3.a,bcy s do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction was 0. by.da,bd3c4a50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a rate of fo .c o.olv5l:hkr 7.0 s. Find the net work done on the boollch..k 5: ovx.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. Howr8r*b:( prsak1 gvg:n much work is re:g:gv*p1rsnra b 8k( rquired to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff6b)5 xt;qg /8uu k(p u,db;z,im noapu objects we might not otherwise be able to liff. Show that the ubpbz d()tu,; ;am u /85p oi6xnq,kugratio 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 izb 6 8k *ou:u)pvz94f-ccdmm 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction ic:i84 od z u9pmf)mz*v6bc u-ks 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 acceler eixo chjz*6,4ation of 0.10 gh*6c4 eijxz o, upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume thy2qfccd;34 plzrg . 9qe distance axis 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, n m6z:kodzv (378jxgevaries as shown in Fig. 6–37. Determine the work done by mj:zg o z7exn(k 83vd6this 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 pa,j e:pps/d v8mrticle 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, .yy7m 9 evlr;.x2pxuilyvz:4with mass of $5.31\times {10}^{-26}$typically has a KE of about$6.12\times {10}^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor1 rb- q6fmrixzse-6z;3da d: e; tka,k 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 o(/ajvtz 6 *fdxd0qt. $(m=9.11\times {10}^{-31}\mathrm{kg})$ which is moving with a speed of$1.90\times {10}^6\mathbf{m}\mathbf{/}\mathbf{s}$ ? $\boxed{{\displaystyle a\times {10}^b\mathrm{J}}}$ a =    b =   

  How much work must be done t/h j*h a)c.gt;,bzpjzqd2/ wr o stop a 1250-kgcar traveling at 105km/h?$\boxed{{\displaystyle a\times {10}^b\text{J}}}$ a =    b =   

  An 88-g arrow is fired from a bow; /qpo7 sz:jxw whose string exerts an average force of 110 N on the arrow over a distance of 78 cmzox;jq: p w/7s. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fieldenabyq kb-qpi.g5.4 h;rkf x6))5p re pr’s glove backward 25 cm when the ball is caught. What was the apkb) p yq;hg4qbr f6- 5na5e).ri p.xkverage force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor p +ogns g:to36will its minimum braking distance be increased, assuming all else is the sat:gsn+p6o 3og me? Ignore the driver’s reaction time.

  At an accident scene on a level rvb0 g(yyt7p6ub :skv :jl0u u,oad, 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) :p7j:v6 l,uy ukbut0bv s (0gythe brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a masj. ol57e81sv b oz(ymos of 0.25 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 durj (8.olo1vey5mzbso 7ing a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who does 80.0 Jk0xw hnjtl) w f;(bmaw 9l.,f6 of work on it? wk ;x)wmfj9hll0a6n.wft(b ,Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a s*bd wps/86rg iac- 1ptingle cable. g/ tcw6i*r 1a-dpb8s pDetermine
(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 constisnc) ()ljok )ant, k, of 440N/m How much must this spring be stretched to store 25 J of potential energ c))si)(lnkoj y?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is thewbv7 )dpv3 t(kl n33y0q-jmq a change in potentiakv3 03wt( 3mqdnl-v ) pyb7aqjl energy?    J

  By how much does the grav:xo0 f8sbj6.wers 7vz+ ku /wcitational potential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m during the jump? 7 wz0ws/okfj+bsue: v.c68r x   J

  A 1200-kg car rolling on a horizontal surface has speed )dwg2ro /5fcp:i zh9h6v1wtev = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffgp v9rct) dh26fe/o:h zw1 w5iness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.20 m aekv nc1-ol3t6/6 fu 4igvob*gbove the ground. What is the potential energyb g4/t lk1 i6g3n*cofevv6-o u 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 16td+,ok0qq3 1 pojr.xb 0utu /n2j(o ua00 m and climbs to the top of a 3300-m p2tn+uqoj3d(0.pur/j0 oxo q u kbt1a,eak.
(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 xc iry:cpk8n; lb+ qjo 1*n/t(hangs vertically next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of theo xtrbk ny8l q;ip(*+jnc 1/c: spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is runnogame8o dcy/b z3u5l3 6a(f5ry ,ib5 ving at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree ivayz 85bmo(g 5ufo3e y6/c3ra b5di, ln 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, slqi3 (4jajtgd 4ides 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 fsxt20 ,z-,nln+f /g5 7,wgpj4bmippzl6m vmo rictionless 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, Frang,6 z+2kp45ywnt3ge (gibs rs ’s kinetic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross bgs6+ ye4w gk2 pr(szg5,tni3the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps qvq/79hgcsogvf 3:)6 :ajeo1 3ck cnovertically upward from the top of a platform with a speed of 5.0 m/s. cf 1h3kj)asvq oo7/6c:g 3 :qng 9veco($\alpha )$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10${}^4$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore f;1 9tl6cyoqm its mass), whose spring stiffness constant is 950N/m is attached to a table ay;tmofl61 q c9nd 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 track shown in : (dei axh8x1pFig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from wha:pe had8 xi1x(t minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffnes.5v lpb6ykk,6h +vijis constant k), Fig. 6–40. The block is given an initial displacemenk. hv ,6ib+ pv6jk5liyt $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungee cord whoscy5x y j k5uhw 6m*8d;7y3h,bvjg 3owue unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, a68dcy*yv jxb,u53 ;w7khm3jhuo g5yw ssuming 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 dr78//+r*lu q+ay s kcy hr6kigs -yvw.cagged up to point 1 where it is released from rest. Ayqi.kwrlv *-ach+g8/r6k/su yyc7 s+ssuming no 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 s41qgb*hq(tz(;o ueuey;t e4 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 designing a spring to be placed 6h .99b9j94/dmakre mfetb ncat the bottom of an elevator shaft. If the elevator cable should break whet j4amcb.f9 e6 mnr9kh9b9/ den 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 cyclc * -5kes0; (2m 7 :qbgquyxspgeol)bfe 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 9( rf:i4e vtdg;wy4z wand traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this collision? wr9wf4:t;i 4yv zed (g$a\times {10}^b$ J a =    b =   

  A 21.7-kg child descends a slide 3. 7p5ohtrnj+e 15 m high and reaches the bottom with a speed of 2.2m/s How much thermjn +1o5pe7hr tal energy due to friction was generated in this process?    J

  A ski starts from rest and slides do,c qk v.f(zy.0hh0/dlo ;es nbwn 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 ground.+br3uf v;3r5gjx7y ov
(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 heih qq:r3; *3mfnfr jcl0ght of 2.0 m, and it bounces back to a height of 1.5 m. frr;qnjm:3 q3 c*f0hl
(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 f)w8cp 1 py(rkconstant horizontal force of 350 N. For the fir(8pcw ry )f1pkst 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. 6–41 passes point 1 with a speed +cv(y2bd4bavd5yvxmw brc9. *w,6 ro of If the average force of friction is equal to one-fifth of ,bwd9 v6acb4.y* rmxyv+cr vwo( 2db5its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12mo7*; q ,sxnraj/s reaches the foot of a steady upward 18.0 ${}^{\circ }$ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly a,( ozk6ut2t*50c zaipd,h9:xkcn fmw ttached 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 turnin9htt ,p0d( a5nfx2,iz: k*cco6k m zwug 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 horizon/j iqg+b )gk4vtal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction isbvq /4ikg)+jg 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 shuttle used a “glider” (2-i vseml0bw+8ix upwzv)x ,2mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider lxsxp, v-8+2vwzi 02b eimuw) 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 17:t xxf3xdp n1g -u7*th8d yx y5lec4e050-W motor to lift a 315-kg piano to a sixth-story window xldxxyne c4u:ettf 08 *-g5h13xy d7p16.0 m above?    s

  If a car generates 18 hp when t(*2zqwo wx o) x/daj3hraveling at a steady 88km/h what must be the average force exerted on the car due to friction and aixo z a(h/3)djowq*2wxr resistance?    N

  A 1400-kg sports car accelerates from rest to 9) 4z gmq0j;v44l4l1shcstici 5km/h in 7.4 s. What is the average powerils414; )jhv 4zsgqt 4c iclm0 delivered by the engine?$\approx$    hp

  (a) Show that one British horseqj70h4mg-ek hmu:z4 w power$\mathrm{ft}\cdot \mathrm{lb}/\mathrm{s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the for7;, krws00g ktzd0a pwm of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times {10}^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times {10}^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 65km/h in abry2v bri1j;m-9m1 v qwgr 7mx5out 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling ax-51bm1r 29gvmr yjmi ;r7qvwt a constant 75km/h.    hp

  How much work can a 3.rg **dt )(wri-rzrq p10-hp motor do in 1.0 h? $a\times {10}^b$ J a =    b =   

  A shot-putter accelerates a 7.3 pofhl9 2yi2f.-kg shot from rest to 14m/s If this motion takes 1.5 s, what average power2 l .2ofyp9ihf was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per mi4pgc t-x8/ hwunute through a height of 3.60 m. What output rating (watts)w4c-hpx tg/ 8u should the pump motor have?    W

  During a workout, the football players at State U. ran up f50y02 2 df+wwre mhe4onk8xxthe stadium stairs in 66 s. The stairs are 140 m long and inclined at an angle of 32 +5frkho2 nefmed xx8004w2yw ${}^{\circ }$. 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 6 t0: jgziv+kag3muk32.0 ${}^{\circ }$ 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 outpuftkxlv.t; 5g 8o6iw* s;,gkz ;ctuv+dt of 120 hp. How steep a hill can it climb at a constant speed of 7zkd6 t 8;l osg iv,t;;+cugkf*x .t5wv5km/h if the frictional forces add up to 650 N?    ${}^{\circ }$

  What minimum horsepower must a motor have t w.u5:td6.iido ne7tto be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coeff5d:ut od.w. i76ttni eicient of friction is 0.45?    hp

  A bicyclist coasts down a +qmn310 i qhewoo7-tzi qbo+ 47.0 ${}^{\circ }$ 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 carsrf8xg ,8l m8 uyu7uw2c have 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 afterlu 7f8ucm,gxr82wu8y 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? $a\times {10}^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the gro( -- 1ng e6adsirw3j7 bhtmi/mund, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work i6r s-i-da1m/ tin(e m3wghb7j s required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the9my5 ,k- ygatf 1936 Olympics shows a5-fymyg9 kt,that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction 3et0fg/eij./2ww b oqalong the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the loop of radius r.je/3oiq. f0e /2 wtbwg
(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 jumpij.:syjqob.b(:rx p3 c ng from an aircraft without his parachute opening. He landed.bc. xs3 j ryb:pj:oq( in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s 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 (Fias1 fl; i acf+1r. k0 i:mues:-pth-wcg. 6–4kumh:t-acp.wsi;l f ca sf0er1 +i :-13).
(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 touwm/xzz1 5it6 onl.q6p of a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevattlo.uixzmz6 /5qn 16 wion 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 elevatortx. 5vkyz06re-/fg qr is 28 m above a huge spring ($k=2.2\times {10}^5\mathrm{N}/\mathrm{m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in Caq(e7hqzoys. (lifornia claims that its lifts can move 47,000 people per hour. If the average lift(oqz h 7y(qes. carries people about 200 m (vertically) higher, estimate the power needed.$a\times {10}^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81 mizzv7u bv,l9f b .z+ru7-x4ay before striking the turbin 9b7xy+7uli u . zzv,z4abf-vre 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 loownkl9pydm8 - 7p (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also wmpy8d9 k 7-nlthat 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 ce;z)1cv (gec aandy bar directly into work, how high could an 82-kg man cli; z vc(ge1ae)cmb a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at -g wt yf);1cqrmjn9e .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 sc spt wk*/yaf41ale, the spring 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 1.0 m, wft k4/sa1*wy phat does the scale read at its peak?    N

  A 65-kg student runs ;- m(zposzr ki k/wkx 5+mn0/eat 5m/s grabs a rope, and swings out over a lake (Fig. 6–45). Hek/ r x-k(n0+ps5emokw i ;z/zm releases the rope when his velocity is zero.
(a) What is the angle when he releases the rope?    ${}^{\circ }$
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athl kp dd:)atm.l3o3 ymbu(a7mav o0x;m8ete climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to accomplism3:apu;o8btay(d . mv)x od0klm7 m3ah this feat?    W

  Some electric-power coi(/90yf ih3i:vfn, acp lw(jwmpanies use water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 h:iaf p wl 9v3nj(,yfc0hii( /wour by a 120-MW ($120\times {10}^6$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in half. What is the sw3 *3 wl / ot7cibrktok.d5iha+a12dlpring stiffness constant for wbta+ 3ko l2t.k715cdawil3ro hi*/deach of the two resulting springs?   k