Page 1 1) A particle of mass 5 kg is acted on by two forces, F = 3 + 4 ...

1) A <strong>particle</strong> <strong>of</strong> <strong>mass</strong> 5 <strong>kg</strong> <strong>is</strong> <strong>acted</strong> on by two forces, F ! = 3ı + 4ȷ N and F ! =
−2ı + 1ȷ N and <strong>is</strong> moved from r ! = 1ı + 1ȷ m to r ! = 5ı − 4ȷ m. What <strong>is</strong> the net
work done on the <strong>particle</strong>?
A) -21 J B) -11 J C) -9 J
D) -1 J E) 7 J
2) A 90 <strong>kg</strong> object <strong>is</strong> initially moving in a straight line with a speed <strong>of</strong> 40 m/s. It <strong>is</strong>
brought to rest by a force providing a constant deceleration. The work done by the force
<strong>is</strong>:
A) -7.2 × 10 4 J B) -3.6 × 10 3 J C) 1.44 × 105 J
D) 7.2 × 10 4 J E) -1.8 × 10
3 J
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3) A single force acts on a body that moves along a straight line. The figure shown <strong>is</strong> a
plot <strong>of</strong> velocity vs. time for the body. During which time interval <strong>is</strong> the magnitude <strong>of</strong> the
work done on the object largest?
A) AB
B) BC
C) CD
D) DE
E) EF
velocity (m/s)!
4.5!
4!
3.5!
D
3!
F
2.5!
2! B
1.5!
1!
C
0.5!
0!
0! 1! 2! 3! 4! 5! 6!
A
velocity vs. time!
time (s)!
E
4) As the figure below shows, a 4.4 <strong>kg</strong> block <strong>is</strong> accelerated by a compressed spring
whose spring constant <strong>is</strong> 640 N/m. After leaving the spring at the spring's relaxed length,
the block travels over a horizontal surface, with a coefficient <strong>of</strong> kinetic friction <strong>of</strong> 0.25,
for a d<strong>is</strong>tance <strong>of</strong> 7.8 m before stopping.
Through what d<strong>is</strong>tance was the spring compressed before the block began to move?
A) 0.131 m B) 0.184 m C) 0.361 m
D) 0.512 m E) Insufficient information has been provided
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5) A mechanic pushes a 2500 <strong>kg</strong> car from rest to a speed V doing 2500 J <strong>of</strong> work in the
process. During th<strong>is</strong> time the car moves 25 m. Ignoring friction, the final velocity <strong>of</strong> the
car <strong>is</strong>:
A) 0.040 m/s B) 1.00 m/s C) 1.41 m/s
D) 4.54 m/s E) 100.0 m/s
6) Juliet <strong>is</strong> standing on a balcony that <strong>is</strong> 6 m above ground level. What <strong>is</strong> the minimum
speed Romeo, standing on the ground, must throw the bouquet <strong>of</strong> flowers to reach Juliet?
(Ignore the effects <strong>of</strong> air res<strong>is</strong>tance.)
A) 8.9 m/s B) 10.8 m/s C) 24.3 m/s
D) 117 m/s E) 150 m/s
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7) The total work required to accelerate a car from 0 to 45 mph:
A) <strong>is</strong> more than that required to accelerate it from 45 to 60 mph.
B) <strong>is</strong> less than that required to accelerate it from 45 to 60 mph.
C) <strong>is</strong> equal to that required to accelerate from 45 to 60 mph.
D) may be any <strong>of</strong> A, B, C depending on the time interval and the effect <strong>of</strong> the
acceleration.
E) may be any <strong>of</strong> A, B, C depending on the force used to accelerate the car.
8) James Bond falls from an airplane without a parachute in pursuit <strong>of</strong> a villain who fell
from the same airplane several seconds before him (the villain has a parachute but has not
yet deployed it). Bond observes that the villain <strong>is</strong> falling at a constant terminal velocity
(having spread himself out), and decides to plunge down head first to catch up with the
villain and wrest the parachute from him. While Bond catches up to the villain, which
Physics 211 conclusion could he correctly infer?
A) The net force on the villain <strong>is</strong> the villain’s weight.
B) The work done by air res<strong>is</strong>tance on the villain <strong>is</strong> negligible compared to that done by
gravity.
C) The mechanical energy K+U grav <strong>of</strong> the villain <strong>is</strong> conserved during the villain’s fall.
D) The terminal velocity <strong>of</strong> the villain would be twice as large if he were half as heavy.
E) There <strong>is</strong> no net work done on the villain.
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9) A 9 <strong>kg</strong> <strong>mass</strong> moves along the x ax<strong>is</strong>. Its acceleration as a function <strong>of</strong> its position <strong>is</strong>
shown in the figure below. What <strong>is</strong> the net work performed on the <strong>mass</strong> by the force
causing the acceleration as the <strong>mass</strong> moves from x = 0 to x = 8.0 m?
A) 80 J B) 160 J C) 353 J
D) 720 J E) 1440 J
10) A 1 <strong>kg</strong> ball <strong>is</strong> loaded into a spring gun with a spring constant <strong>of</strong> 10 5 N/m. If the
spring <strong>is</strong> compressed by 0.1 m and the ball <strong>is</strong> shot up vertically, how high does it r<strong>is</strong>e into
the air?
A) 12.7 cm B) 1.3 m C) 12.7 m
D) 102.0 m E) 51.0 m
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11) A 1000 <strong>kg</strong> block <strong>of</strong> granite <strong>is</strong> pulled up an incline 30 m high and 40 m in horizontal
length at a constant speed <strong>of</strong> 2 m/s by a cable and winch. The coefficient <strong>of</strong> kinetic
friction between the block and the incline <strong>is</strong> µ k = 0.4. What <strong>is</strong> the power due to the
tension force in the cable?
A) 20384 W
B) 24131 W
C) 9016 W
D) 6112 W
E) 18032 W
12) A small, 0.1 <strong>kg</strong> rubber ball <strong>is</strong> dropped at rest from a height <strong>of</strong> 3 m, bounces <strong>of</strong>f the
floor and rebounds to a height <strong>of</strong> 2.5 m. What <strong>is</strong> the magnitude <strong>of</strong> the impulse <strong>of</strong> the floor
acting on the ball? (Hint: find the velocity <strong>of</strong> the ball just before and just after the
coll<strong>is</strong>ion with the floor, and consider the direction <strong>of</strong> each velocity.)
A) 0.067 <strong>kg</strong> m/s B) 0.49 <strong>kg</strong> m/s C) 0 <strong>kg</strong> m/s
D) 1.47 <strong>kg</strong> m/s E) Impossible to determine since the coll<strong>is</strong>ion <strong>is</strong> inelastic.
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13) A conservative force F(x) acts on a 2.0 <strong>kg</strong> <strong>particle</strong> that moves along the x-ax<strong>is</strong>. The
potential energy U(x) associated with F(x) <strong>is</strong> shown in the figure below. When the
<strong>particle</strong> <strong>is</strong> at x=10.0 m, its velocity <strong>is</strong> 3.16 m/s. Between what limits <strong>of</strong> x does the <strong>particle</strong>
move?
U(x) (J)
5
0
-5
-10
-15
-20
-25
0 5 10 15 20
x (m)
A) x min = −∞, x max = +∞ B) x min = 0 m, x max = 20 m
C) x min = 5 m, x max = 15 m D) x min = 7.5 m, x max = 12.5 m
E) The <strong>particle</strong> remains at x min = x max = 10 m
14) A 4 <strong>kg</strong> <strong>mass</strong> moving at +6 m/s undergoes a one-dimensional elastic coll<strong>is</strong>ion with
another 1 <strong>kg</strong> <strong>mass</strong> moving at −4 m/s (in the direction opposite to that <strong>of</strong> the greater <strong>mass</strong>).
What <strong>is</strong> the magnitude <strong>of</strong> the change in momentum <strong>of</strong> the 4 <strong>kg</strong> <strong>mass</strong> as a result <strong>of</strong> th<strong>is</strong>
coll<strong>is</strong>ion?
A) 32 <strong>kg</strong> m/s B) 16 <strong>kg</strong> m/s C) 8 <strong>kg</strong> m/s
D) 4 <strong>kg</strong> m/s E) 2 <strong>kg</strong> m/s
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15) A car travels around a circular unbanked curve at the maximum speed without
skidding <strong>of</strong>f the road. Which <strong>of</strong> the following statements, if any, <strong>is</strong> false?
A) The centripetal acceleration <strong>is</strong> provided by the friction between the tires and the road.
B) There <strong>is</strong> no work done by the radial component <strong>of</strong> the friction force between the tires
and the road during the turn.
C) The radial component <strong>of</strong> the force <strong>of</strong> friction between the tires and the road during the
turn <strong>is</strong> the weight <strong>of</strong> the car multiplied by the coefficient <strong>of</strong> static friction between the
tires and the road.
D) During the turn, the direction <strong>of</strong> the car’s acceleration vector changes with time.
E) All <strong>of</strong> these statements are true.
16) Which <strong>of</strong> the following graphs <strong>of</strong> the kinetic energy as a function <strong>of</strong> time <strong>is</strong>
physically impossible?
A) K
B)
K
0
t
0
t
C) K
D)
K
0
t
0
t
E) All <strong>of</strong> the above are possible
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17) An old Chrysler with <strong>mass</strong> 3000 <strong>kg</strong> <strong>is</strong> moving along a stretch <strong>of</strong> road at 72 km/h. It <strong>is</strong>
followed by a Ford with <strong>mass</strong> 2000 <strong>kg</strong> moving at 90 km/h. How fast <strong>is</strong> the center <strong>of</strong> <strong>mass</strong>
<strong>of</strong> the two cars moving?
A) 81.5 km/h B) 90.0 km/h C) 79.2 km/h
D) 72.0 km/h E) 7.2 km/h
18) A 4000 <strong>kg</strong> truck <strong>is</strong> at rest at an intersection, waiting for a green light (with no other
vehicles around). It <strong>is</strong> a snowy and icy day, with no friction on the road. A 1000 <strong>kg</strong> car
traveling at 5 m/s strikes the stopped truck square on from behind. The bumpers <strong>of</strong> the
two vehicles lock together as a result <strong>of</strong> the coll<strong>is</strong>ion, so that they skid across the
intersection together. How fast are they traveling?
A) 1.0 m/s B) 5.0 m/s C) 0 m/s
D) 2.5 m/s E) Impossible to tell since the coll<strong>is</strong>ion <strong>is</strong> not elastic
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19) The Earth has a <strong>mass</strong> <strong>of</strong> 5.98×10 24 <strong>kg</strong> and travels around the Sun once a year (365.25
days) in a roughly circular orbit <strong>of</strong> radius 1.49×10 11 m. How much kinetic energy does
the Earth have?
A) 1.77×10 29 J B) 2.63×10 33 J C) 5.86×10 25 J
D) 6.67×10 43 J E) 3.14×10 51 J
20) An object has an initial (t = 0s) momentum <strong>of</strong> 20 <strong>kg</strong> m/s. It moves under the
influence <strong>of</strong> a force varying with time as per the plot below. What <strong>is</strong> the object’s
momentum at t = 8s ?
10
5
F (N)
0
-5
-10
0 2 4 6 8
t (s)
A) 50 <strong>kg</strong> m/s B) 35 <strong>kg</strong> m/s C) 20 <strong>kg</strong> m/s
D) 0 <strong>kg</strong> m/s E) -10 <strong>kg</strong> m/s
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Answer key
1) A
2) A
3) C
4) D
5) C
6) B
7) A
8) E
9) D
10) E
11) E
12) D
13) D
14) B
15) E
16) C
17) C
18) A
19) B
20) C
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