In what ways is the word “work” as used in everyday fe64ovw0g; l zlanguage the same as that defined in physics? In what ways is it different? Give exaf06l gw;zvo4emples of both.

Can a centripetal force ever do work on an obc7./z9agcv t qject? Explain.

Can the normal force on an object evox0) xi wn/oc8er do work? Explain.

A woman swimming upstream is not moving with respect to the shore. Is q29or;pg/qg v she doing any work? If she stops /; rp9qv qggo2swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces alwa;v/i g9b8 q9 8qvc(hs ls3srioys negative? [Hint: Consider what h/ 9;qhq(irgbcoil v893 vss 8sappens to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wa *-04w0ftotb cn r 8q25akagxfll even though you are doing no work?fr ano0*txafg k8wtq0bc 52-4

You have two springs that are identical except that spring l is stiffer thanhu (r)5n ubfql b/k:1c sprb1: )q5/h nurb cklfu(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 horizontal foavq oi3sq2,q/lbodwj6, ; r*a rce on a block that is free to slide on a frictionless surface (Fig.6-30),v ,/oaodsjq ;alb i*362qqwr. 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 poq.v t(5* gp efqctn))ltential energy change when you jump as c(nq)vte f*5q g t)lp.high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, a fkb(qxy98+xpll with the same speed but with different launch angfpbq 9kxy x(8+les. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above yp vk 31t+cjq9its lowest point in two different+qv3t j9pcky 1 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. 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 taba. + un,)vf7l;d4h lqhz :wwehle. If you compress the spring by pressing down with your hand anhvu zw+)7hnq,edhw .:al4l; fd then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceilik czd7f,.c(45im dpmf ng 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 th 7cd,cp.kiffmdm (4z 5e ball without pushing it. Why?

What happens to the gravitational potential energy when water at the top o/ zajnmt24n7ihl b5r 8f a waterfall falls to the pool belomrzj8 2h/tann7 4 il5bw?

Describe the energy transformations when q q grfiy:j90w6e3e /na child hops around on a pogo stick.

Describe the energy trans,b;jkxztg1c 4 formations that take place when a skier starts skiing down a hill, but after a time is brought to rest by strijk4xt;zc, g 1bking a snowdrift.

A child on a sled (total mass m) starts from rest at thelmp3p9/0 w cpcabr5y; top of a hill of height h and slides down. Dmw/l350p9 apc py;r bcoes 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 ffnz+ xve45h )lallen log in their path rather than stepping on top and jumping down on the other + e)xfl4v5znhside. Explain.

Two identical arrows, one with twice the speed of the othercfdte*jx7q-d 5 6aje 5, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Etaeq 5c* 756jdfed -jxxplain.

Analyze the motion of a simple swinging pendulum in terms of energy, (a) ign- r9datzj 6:)ha/jcntw lul20 h e0d0eoring friction, and (b) taking friction into account. Explain why a grandfatc9)2w u e nza0:tthhe60ldj-dl0arj/her clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greatezljk6w y(v9f/ r than its originaj6vy 9 (/kfwzll height? Explain.

Suppose you lift a suia3 po,rpy -k0ztcase from the floor to a table. The work you do on the suitcase depends on which of the followi-opyk,a0p3 r zng: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the powb l1: ie+ 7 -jtxk1g1e e8ctlhpcmci.8er needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail th ayf.o. vdci-3an to climb straight up?-f3va y.c .iod

Recall from Chapter 4, Example 4e +cb/7)ah : piqug7jh–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 beu7 hjpq/h ie)ab:c7 +g pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a o,fo/d7th7 f c265-kg pile driver falls 2.8dc/ht7,fo7 fo0 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.sm0,v ht y1+ae0 m high. How much work is required?sayh+1te0, m v    J

  A 1300-N crate rests on the floor. How much wo1li+ ok6l k(dupc m/oej9k2 (urk is required to move it at constant speed (a) 4.0 m along the floor against a friction forc mol91(jok lekucp6+ /2ikdu( e 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 m4xc (n 8c. (b jowlt6kv-k+:bbfqqll6 across a rough floor without acceleration, if q. wkckv6llxbt b 4f:o(8-6n +l (bcjqthe effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a)wm7 :z 3,vlybvnom(1r lb k.z floor at a rate of for 7.1w m.o krv3y 7n, z)lbblmz:v(0 s. Find the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, li; q7 cwv9vtphpixc9un- :2b /ge flat on a table. How much work is required to w:9 pcp xiqu vbc-9;hgt 7nv2/stack them one on top of another?    J

A lever such as that siwthf-h2 rb 97; sy)gnhcy9b :hown in Fig. 6-35 can be used to liff objects we might not othetg2i 9h )n:h by whbs-f;y79crrwise 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 acceleratingqz g5np70y0br by a man who is pushing back on it parallel to the in rpzn07ygq0b5 cline (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+nf .3hvj1 chw of mass M an acceleration of 0.10 g upwajh v+fw1hn3c. rd.    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 th5x -cwt0)uu s9 4znxecn u5-vne 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, varies as shown in Fig. s94.-f)dhwm +pkxyq/ glmgto:ie 2c +6–37. Determine the work done by this force to move thch/ m9y4txp2+e)+:ok-qsmig d.w gl fe 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 partiawoe 2j*gu7ms8.+f7izj8 uhz cle 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 ms8d q gy;cqk2:ass 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 spxqgzw5 h/ g 9:+w7 9zjtfvtrpm8y 3wt(eed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to st1w xcmzbwc) rm ml68r)k v0t0,op 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 traveling at 105) tb .pbrj4 -lrez095h(ktuyukm/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired mdk2w* . dr;e.okegi 7from a bow whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is tho2g7kd;der. emwik. * e speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25 cm ww5 ji)m d4-: clpghb8ahen the ball is caught. What was the averagp i)g:jd5-4bwl 8h amce force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what a/i2 z rk(2(aihlav4ffactor will its minimum braking distance be increased, assuming all else is the same? Ignore the driver’s reac2z aa(kiri4 f hal(2/vtion time.

  At an accident scene on a level rx3wt6 6fxk 0/r , gvwz/bu0qjjoad, 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 slawxftwzxq0v ub0, 36k gjj6r//mmed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time it reaches the gvrp)r2( c vbm*f0byb9 s;.p cplate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about*.cb (br f 0ygr;c bppv)2m9sv 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who does 1 9yexwxfz - fclg(c-680.0 J of work on it? Neglect air resistance.xfwg9x--f1czl( y c e6    m

  A 285-kg load is lifted 22.0 m vertically wf8.r5apv.uxu9 cjq - bith an acceleration by a single cab5r -9 u.xbuqva.8j cpfle. Determine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, ofb/ 3e*g5vtey 4lqdz,i 440N/m How much must this spring4, dq5*e/z t3ivylegb be stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to anothqcjk 3m z5gdcf8j:0e :er 1.2 m higher. What is the change in potential ener8:e 3:dcqmfz0jjg k 5cgy?    J

  By how much does the gravitational potent,jn nczfjse+7p t6ft: 7ho 5u:ial energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m during the jutct,osh fejf75: pn6n: jz+u 7mp?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h when cj7 wsg6f -2k6ljpis n,s;gr k)ar7q* it strikes a horizontal coiled spring and is broughp6*wss 2 7,k6sc-nkr7ijf q ag)lg;r jt 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 so it is 2.20 m sm,wsowdaz0 x+ i q2zo :k-b)0above the ground. What is the poz a, -dm k:wib02s+wox0 sq)zotential 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 thek6o *a.ad+ldwzzc::y top of a 3300-m peak. dl:aa+cyz.od* w6:kz
(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. The1ty,0zsst x g;aqr 7c 9.*owui 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 the spring, where will the end;gcywzus atix ts07q9,1* ro. of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is runni)g46 lotblj4 lng at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing upward? 4l4tolb) jl6 g   m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, startinvl4:dpq v/1 01h+xbnmvqmt *dg from rest, slides 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 frictionl71cu hy46 leydkavd4)ess 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 tran w+/bkzh:rt9uisa*9 n ; v7wpq2 a,iensformed 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 the bar wi9krw7, 2t+pz iu;* naqw: snviah eb/9th a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertf-dz mh4 cfqc 0e b9z+wf-bb9+ically upward from the top of a platform with a speed of+f0fd- mewb 4czhz-bc bf9q+9 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 stiffnhz.y4 pwe71z gjgq.z/ ess constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can i. zjgw4 zy7q.pz g/h1et 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 mey i )0ettw:la425vw5d.hg j1ke+e; qd/v hjthe looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top oljt1v/ 4geee:2ehk5 ;d0yv5iqaw)hjm +tdw .f 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 consta6(br*ptx,xdfs +h7 ucy + eu5gnt k), Fig. 6–40. The block is given an initial d* 5ru+t(,xsb gup dy h6fx+ec7isplacement $x_0$ 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 who 7bj nq tkb8x2k:cdb6s 2;6tjrse unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. t:;bt8b6cs2jkkbx j 7dq 2n r6$\approx$    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 point 1 where i 1n ;4bx;r k .,ivd/sy-qa1ojuncq6 yvt is released from rest. Assuming no friction, calculatkiu,qq/. ncydors -x bva1jnvy;14; 6e 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 an axu7-m.35x s0fkfvg6 p ajwsz. ngle 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 desig;y/qr/8yo lch ning a spring to be placed at the bottom of an elevator shaft. If thehr cl/yq ;/oy8 elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up a 7.85 36yw jz:znzs $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 95km/h in opposite direct9ipihx. 2s o4p9o-ya ,mdurm9ions, collide head-on and come to rest. How much thermal energy is produced in this ci4hmp9o.sipmo 9dr 9 ,yua-2xollision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide ct-)je )rwhu w1b0nfcu* xo/mdzr6;. 3.5 m high and reaches the bottom with a speed o 1oud6u /)*wtf zr)c;emb -x0wnc.r jhf 2.2m/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and yxc0, q2*ayxxslides 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 fro h-gkag:g (t3m3+fsht m 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 height of 2.0 m, and it bounces back to a heig37.b hhy c.jf+jp d.qqht of 1.5 m. p7 +.dh jq hjbc..fq3y
(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 fromup+ bisus2u6 * rest, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the cr b su+si62pu*uate?    m/s

  Suppose the roller coaster in Fig. 6–41 pass24 nnngh/baz sxpt0/ 1es point 1 with a speed of If the average force of friction isx n z2gn4n1/pab0hst/ equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady upward 18.0 d)hdgwoas+ 8smz2 j; *pqn. o uf.-tj;$^{\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 firwfl 43p z)3/gl5gn wqktx q+g,9f dms+mly 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 posiz 34q,+ ff+3w qm sg)wt/g5gp n9ldxlktion 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 lightuuj0gngm (yc07g v: ;v horizontal spring, Fig. 6–40. The block can slide along a table where the coefficie0u70guy;cgn:(vm jg v nt of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights f dkyr .-ehl)5gap(.:hxg2nr bor the space shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistan (l .h)h-g g.prd2kbae:5xyrnce?$\approx$    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 tow*4t vr v i,hsh(ffoi)5x8h;o lift a 315-kg piano to a sixth-story window 16.0 m abthv4if5 xhworh f;*)oiv s,( 8ove?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be the a6y0a blkkvx;q9i* ))v uyhxm6verage force exerted on the car due to fy ;9xv6mvkqk0 6*uhxa) )ylibriction and air resistance?    N

  A 1400-kg sports car acc6zd wax--3st/y* kxzv elerates from rest to 95km/h in 7.4 s. What is the average power delivered by the engdzyx/ w*k -a z-xs63tvine?$\approx$    hp

  (a) Show that one British horsepowe ql+c;gcg-)cf 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 form of “kilowat),ow.a1dak+ bfz mdb5 t-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 -t7u8vtplqrr)u+ca 4from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) ist7v4 8t)rur+- cap qlu needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in3jb;tvao*y0 gb rzn a.ykd q*gp-25-k 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7pj*z0 eios6hu pt 4cm9;2cur2.3-kg shot from rest to 14m/s If this motion takes 1.5 srm c ze4 i920*chu6;opjtu2 ps, what average power was developed?$\approx$    W

  A pump is to lift 18ays8v5,*kua vko,7 zoo grg:5.0 kg of water per minute through a height of 3.60 m. What output rating (watts) should the pump motor hu5g7k zra 8*os,voky:g,ao v 5ave?    W

  During a workout, the football players at State U. ran up theo.yvf1wvi6lh d9+edq18d t6s fw) o1d stadium stairs in 66 s. The stairs are 140 m long9.6ffwi e+ hvdso 1yl1ow q) 8dtvd6d1 and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist ey)dk 8n 1kns1(jq )rfclimb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximuj+z5(dsz ex,km power output of 120 hp. How steep a hill can it climb at a constant 5s+j (xzez kd,speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motr;g0ayiywylv:0e p37 or have to be able to drag a 310-kg box along a level floor at a speygila;:0 vy07prw3 eyed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down 1:agyebqj- z ;e2-/w ng0lgfv a 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built h.6jofqfk 3g 5x*yu7 y“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 co. y6yf7*uf qj5g3khoxmpression 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 firsr, i0s8 lh.qlvblf+.ip i/,qds w.yi -t shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass owq.i+b.y-q s irf /isi, pl 0,dl.lv8hf 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 jump (Fig. 6–42) in the 1936 Olympics 5dc o47gx0rzhx06ujw shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need aw5xd7uh 6c40o rj 0xgzt 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 alo.mpnt3dn2-0oa w lt;wf0xgxp;/mig1 ng the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the ltfnt a ;w2wxnlgo/g.dpi 0;10-mx mp3 oop 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 aircw(erv,tc f+ vj fsupub ( -.q/:u86aneraft 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 wabeav -fscw+8 jut:p(/ uveun .f ,q6r(s 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 fixe:o,fbopm5ljy4oio((k l0d m16 f j*uzd (Fig. 6–43). p 4bk:0(offym l(*joozld,u o i1j5m 6
(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 1 s t592e6glhq0qz2 pc6waumhof a 3700-m-high mountain. The climb is made in 5.0 h starti9hz2q6acq w stg 6eh p2u15m0lng 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 elevato h c va/ykv0q0-bwhk811eg/nj5z: vinr is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifn6. l,r ,vwvzpts can move 47,000 people per hour. If the aver z 6plr.vv,w,nage lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at theny rlh/-e osg0/-(qx t; pt7u9wdbm.q rate of 650kg/s and falls vertically 81 m before striking the turbi-. ;nxs/theym(upt-q 9owld/qgbr7 0ne 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 coalwlmdmt zd9z vw6y1y, .447iu ster with a circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long a d.4w 147yd9zi6mwlm, v lyztus 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 d 9d0 v b(1.wh+ km+f5pdvnhwvwork, how high could an 82-kg man climb a ladder if he were fueled by one bar+hvn9vhfw 05w kbdm . d(+p1vd (=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 angle / -gidvq xn9dpf09j:sof 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 in,9 jykndv 65cf8qaao7 side the scale compresses 0.60 mm, and i,fn d5aj89vkoc7qa6 yt tells 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 rope, and swing 0h;c+4 5owjz8cx s1pw(pn cbhs out over a lake (Fig. 6–45). He releases the rope when his velocity is zero. (jw +85hppn sw;c bo04zcx1hc
(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 vertica vqgdj7dz u7 qft61k)fdt.92zl distance of 5.0 m in 9.0 s. What minimum power output j9t7.2vq71 ddqg fk 6ztd) zfuwas used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumped bwe7,r4u. tobtqe uu0*mep ./ty reversible turbine pumps from a low totebmqeu.etpw0rt4 / u *7u.o, a high reservoir. 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. Wgm:i0/a rkcm *hat is the spring stiffness constantkc0ia* m/gmr: for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.fg,0v*j7r ;oou3r f u w6x-h/lx:wq pz0 m 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 accelerate fro*e9h *ptouz0h-7jsc- vl,z sej8 6mlzm 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to-z*-e,hh 0z p*9 sstje7ol6jvczl mu8 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function do3 a5f.dh.gj(the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estim faddoj 53h..gate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertical*tboce b;v*ph. n.1 kaly upward a distance of 500 m, what was its velobe*1n .b*.v otc pha;kcity when 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 c+h*p. d 3i t etzmbkee4vqf-h8c -wg64qh/s6wheel from a height of 2.0 m at a rate of 95kg/s (a) If tq.eecv/w i bgkp46qh-3f *-zhmst4h+8ectd6his water wheel is set up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s