PHYS 2421 EXAM #3 Friday, October 25, 2013

work any four (4) of the followint problems from Chapter 7:

1. A 0.50-kg obiect moves in a horizontal circular track with a radius of 2.5 m. An external forceof3.0 N, always tangent to the tracl! causes the obiect to speed up as it goes around. The wo.kdone by the external force as the mass makes one revolution is:

A) 7.s J

Bl 24!,-c) 47D

D) 94JE) 720 J

2. A particle moves 5 m in the positive x diredion while being acted upon by a constant force

-8)

c)D)

E)

F = (+ N.!i * (z rui) - (a ru) [. the work done on the particle bythis force is:

:'A) 20.J '

10J

-20 )30Jis impossible to calculate without knowing other forces

,, 3: A 10&kg piano rolls down a 20" incline. A man tries to keep it from acceleratin& andi'manages to keep its acceleration to 1.2 m/s2. lfthe piano rolls 5 m, what is the net work doneon it by allthe forces acting on it?A)60JB) 19!-!

1t1 ooo r)-D)TO00 J

E) 4900 J

4. A 0.50-kB object moves in a horizontal circular track with a radius of 2.5 m. An external forceof 3.0 N, always tangent to the track, causes the objed to speed up as it goes around. lf ,t startsfrom rest its speed at the end ofone revolution is:

A) 5.5 rn1s

B) 14 m/s)- c) t5 m/s

D) 18 m/sEl 27 mls

5. A man pushes an 80-N crate a distance of 5.0 m upward along a frictionless slope that makes

an angle of 3OP with the horizontal. His force is parallelto the slope. lfthe speed ofthe cratedecreases at a rate of 1.5 m/s2, then the work done by the man is:

A) -2@ J

a) 61r \c) 140 |D]-00 iE) 400 J

PHYS 2421 EXAM f3 Friday, octobet 25, 2073 NAME

,,6. A man moves the 1Gg obiect shown in a vertical plane at a constant speed from position X

to position Y along a circular track ofradius 20 m. The process takes 0.75 min. The work doneby the man is about:

oli.dA) 1Jq).2-le) 4,D) 6JEI L2J

7. An idealsprin& with a pointer attached to its end, hangs next to a scale. With a 1fi)-Nweight attached, the pointer indicates n40" on the scile as shown. Using a 20GN weightinstead results in "50" on the scale. Using an unknown welght X instead results in "30" on thescale. The weight of X is:

A) 20NB) 30NCIll{)Nqlo N

E) 7sN

8. An ideal spring is hung vertically from the ceiling, When a 2.&kg mass hangs at rest from itthe sprint is extended 6.0 cm f.om its relaxed length. An upward externalforce is then appliedto the block to move it upward a dlstance of 16 cm. whlle the block ls being ralsed by theforce, the-wq* done by the spring isAl -7-O J _//s) -o.saJc) -0.26 J

D) 0.s2 J

E) 1.0J

Y

\ix

PHYS 24a!EXAM #3 Friday, October 25, 2013 NAME

l!). 'e l.s kc .rrt" t llr from a height of 2.0 m onto an industrial spring scale with a spring

;onstant of 1.5X1Os N/m. At its greatest compression the reading on the scale is:

A) 1sNB) 29Nc) 1.s 81d N

D) a.1E]{E_N,e1 g.oB1q9

10. An escalator is used to move 20 people (60 kg each) per minute from the first floor of a

department store to the second floor, 5 m above. The power required is approximately:

A) 100 wB) 200rd_\c) 1000 w )

-- Di-zooo wE) 60,000 w

11. A 5O-N force is the only force on a 2-kg crate that starts from rest. At the instant the crate

has gone 2 m the rate at which the force is doing work is:

A) 2.s WB) 2sWc) 7swD)_4qU_El oow )12. A mass of47 kg is moving horizontally as a force of 190 N, direded at 25" below the

horizontal, is exerted on it. When its speed is 7.3 m/t what is the rate at which the force is

doingwork?

A)0 wB) 340 Wc) s90t&Dllio0-EE) 1400 W

PHYS 2421EXAM #3 Friday, Octobe. 25, 2013 NAME

work eny iour (4) of the tollotylng ptoblems frofi Chaptet 8:\ ., 1. The long pendulum shown is drawn aside until the ball has risen 0.5 m. lt is then given an

Initialspeed of 3.O m/s. The speed ofthe ballat its lowest position i5i

A) 0 m/s8) 0.89 m/sC) 3.1mlsD) 3-7EliE) 4.3 m/s

-\2- A 0.50-kg block attached to an ideal spring with a spring constant of 80 N/m oscillates on a

horizontalfrictionless surface. when the spring i5 4.0 cm longerthan its equilibrium length, thespeed ofthe bloct is 0.50 m/s. The greatest speed ofthe block is:A) 0.32 m/sB) 0.55 m/s

. c) 0 4 m1_s-)

D) 0.87 m/sE) o.93 m/s

3. A 700-N man jumps out of a window into a fire net 10 m below. The net stretches 2 m

before bringingthe man to rest and tossing him back into the air. The maximum potentialenergy of the net, compared to its unstretched potential energy, is:

A) 300 J

B) 710Jc) 8s0,D) 7q00 J-

E) 84OO J'\

4. A toy cork gun contains a spring whose spring constant ls 10.0 N/m. The spring is

compressed 5.00 cm and then used to propel a 6.00-g cork. The cork, however, sticks to thespringfor 1.00 cm beyond its unstretched length before separation occurs.Ihe muzzle velocityof this cork is:

A) 1.02 m/sB) 1.41mlsC) 2.00 m/sol 2.o4 mlsE) 4.00 m/s

- _'L0.5 rh-T

PHYS 2421 EXAM f3 Friday, October 25, 2013 NAME

5. The string in the fiSure is 50 cm long. When the ball is released from rest, it swings along the

dotted arc. How fast ls it going at the lowest point in its swing?

A) 2.0 m/sB) 2.2 m/sc) 3-1 m/s ,)

D) 4.4 m/sE) 69.m/s

I ,6 The potentialenergy of a 0.2ckg particle moving along thex axis is given by

U(xl =.8.0 !ln2l* + (2.0 Jlmalf '

when the panicle is atx= 1.0 m it is traveltng in the positlvex direction wlth a speed of 5.0

m/s. lt next stops momentarilyto turn around atx =A) 0mB) -1.1 mcIafii\D) -2.3 mE) 2.3 m

7. A stationary mass m = 1.3 kg is hanging from a spring of spring constant k = 1200 N/m. You

raise the mass a distance of 10 cm above its equilibrium position. How much has the potential

energy ofthe mass-spring system changed?

A) 1.3 J

B) 6.0 J

ct z.s.r)-- ifiz J

E)13J

8. A 2.2-kg block starts from rest on a rough inclined plane that makes an angle of 25o with the

horizontal. The coefficient of kinetic friction is 0.25. As the block Soes 2.0 m down the plane,

the mechanical energy ofthe Earth-block system changes by:

A),! r _Bi -4.8 J . )c) 9.8 J

D) -18 J

E) 18J

*t

PHYS 2421 EXAM T3 Friday, October 25, 2013 NAME

9. A s-k8 projectile is fired over level ground with a velocity of 200 m/s at an angle of 25 o

above the horizontal. Just before it hits the ground its speed is 150 m/s. Over the entire trip thechange in the thermal energy ofthe projectile and air is:A) +6300 J

B) -6300 J

Cl +44,000 Jo) -44,000 J

E) 0.,

10. A 0.75-kg block slides on a rough horizontal table top. Just before it hits a horizontal idealspring its speed is 3.5 m/s. lt compresses the spring 5.7 cm before coming to rest. lfthe sprlnSconstant is 1200 N/m, the thermalenergy of the block and the table top must have:A) not changed8) decreased by 1.9 J

C) decreased by 2.6 J

D) increasedby-tg J

E) increased by 2.6)

11,. A stationary mass rn = 1.3 kg is hanging from a sprlng ofspring constant * = 1200 N/m. youralse the mass a dlstance oflO cm above its equlllbrium position in a time of 1.4 s. What wasthe average power expended?A) O.93 Ws)4.3w-c) s-2 wD) 8.5 WE) 10.2 W

12. The energy of a system increases at a rate of 3.5 t+ 6-2 4 ihjoules- What is theinstantaneous power at t= 3.1s?A) 3.s WB) 6.2 Wc) 16W -D)42WE)70W

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