Download Physics 125 Practice Exam #2 Chapters 4

Physics 125
Practice Exam #2
Chapters 4-5
Professor Siegel
Name: __________________________ Lab Day: _____________
1. With one exception, each of the following units can be used to express mass. What is
the exception?
A) newton
B) slug
C) gram
D) N•s2/m
E) kilogram
2. Which one of the following terms is used to indicate the natural tendency of an object to
remain at rest or in motion at a constant speed along a straight line?
A) velocity
B) inertia
C) acceleration
D) equilibrium
E) force
r
3. A net force F is required to give an object with mass m an acceleration a. If a net force
r
6 F is applied to an object with mass 2m, what is the acceleration on this object?
r
A) a
r
B) 2 a
r
C) 3 a
r
D) 4 a
r
a
E) 6
4. When the net force that acts on a hockey puck is 12 N, the puck accelerates at a rate of
48 m/s2. Determine the mass of the puck.
A) 0.25 kg
B) 1.0 kg
C) 5.0 kg
D) 2.5 kg
E) 2.0 kg
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5. A net force of 25 N is applied for 5.7 s to a 12-kg box initially at rest. What is the
speed of the box at the end of the 5.7-s interval?
A) 1.8 m/s
B) 12 m/s
C) 3.0 m/s
D) 7.5 m/s
E) 30 m/s
6. A 2150-kg truck is traveling along a straight, level road at a constant speed of 55.0 km/h
when the driver removes his foot from the accelerator. After 21.0 s, the truck's speed is
33.0 km/h. What is the magnitude of the average net force acting on the truck during
the 21.0 s interval?
A) 2250 N
B) 626 N
C) 1890 N
D) 972 N
E) 229 N
7. Two forces act on a 16-kg object. The first force has a magnitude of 68 N and is
directed 24° north of east. The second force is 32 N, 48° north of west. What is the
acceleration of the object resulting from the application of these two forces to the
object?
A) 1.6 m/s2, 5.5° north of east
B) 1.9 m/s2, 18° north of west
C) 2.4 m/s2, 34° north of east
D) 3.6 m/s2, 5.5° north of west
E) 4.1 m/s2, 52° north of east
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Use the following to answer questions 8-9:
r
A force P pulls on a crate of mass m that is in contact with a rough surface. The figure shows
r
the magnitudes and directions of the forces that act on the crate in this situation. W represents
r
r
F
the weight of the crate. N represents the normal force on the crate, and f represents the
frictional force.
8. Which statement best describes the motion of the crate?
A) The crate must be at rest.
B) The crate must be moving with constant velocity.
C) The crate must be moving with constant acceleration.
D) The crate may be either at rest or moving with constant velocity.
E) The crate may be either at rest or moving with constant acceleration.
r
F
9. What is the magnitude of N , the normal force on the crate?
A) 57 N
B) 80 N
C) 160 N
D) 196 N
E) 230 N
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10. A crate rests on the flatbed of a truck that is initially traveling at 15 m/s on a level road.
The driver applies the brakes and the truck is brought to a halt in a distance of 38 m. If
the deceleration of the truck is constant, what is the minimum coefficient of friction
between the crate and the truck that is required to keep the crate from sliding?
A) 0.20
B) 0.30
C) 0.39
D) 0.59
E) This cannot be determined without knowing the mass of the crate.
11. A boy pulls a 5.0-kg sled with a rope that makes a 60.0° angle with respect to the
horizontal surface of a frozen pond. The boy pulls on the rope with a force of 10.0 N;
and the sled moves with constant velocity. What is the coefficient of friction between
the sled and the ice?
A) 0.09
B) 0.12
C) 0.18
D) 0.06
E) 0.24
Use the following to answer questions 12-14:
A block of mass M is held motionless on a frictionless inclined plane by means of a string
attached to a vertical wall as shown in the drawing.
12. What is the magnitude of the tension in the string?
A) zero newtons
B) Mg
C) Mg cos θ
D) Mg sin θ
E) Mg tan θ
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13. If the string breaks, what is the magnitude of the acceleration of the block as it slides
down the inclined plane?
A) zero m/s2
B) g
C) g cos θ
D) g sin θ
E) g tan θ
14. Assume the plane is not frictionless and the string breaks, what minimum value of the
coefficient of static friction, μs, would prevent the block from sliding down the inclined
plane?
A) zero
B) 1
C) cos θ
D) sin θ
E) tan θ
15. A ball moves with a constant speed of 4 m/s around a circle of radius 0.25 m. What is
the period of the motion? [Hint: For this calculation, you need to know the
circumference of the circle.]
A) 0.1 s
B) 0.4 s
C) 0.7 s
D) 1 s
E) 2 s
16. The second hand on a watch has a length of 4.50 mm and makes one revolution in 60.00
s. What is the speed of the end of the second hand as it moves in uniform circular
motion?
A) 9.42 × 10–4 m/s
B) 2.67 × 10–3 m/s
C) 5.34 × 10–3 m/s
D) 4.71 × 10–4 m/s
E) 2.36 × 10–5 m/s
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17. Approximately one billion years ago, the Moon orbited the Earth much closer than it
does today. The radius of the orbit was only 24 400 km. The orbital period was only
23 400 s. Today, the average radius is 385 000 km; and the present period is 2.36 × 106
s. Assuming that the orbit of the Moon is circular, calculate the ratio of the speed of the
Moon in its ancient orbit to the speed that it has today.
A) 15.8
B) 12.8
C) 10.2
D) 7.15
E) 6.39
18. A rock is whirled on the end of a string in a horizontal circle of radius R with a constant
period T. If the radius of the circle is reduced to R/3, while the period remains T, what
happens to the centripetal acceleration of the rock?
A) The centripetal acceleration remains the same.
B) The centripetal acceleration increases by a factor of 3.
C) The centripetal acceleration increases by a factor of 9.
D) The centripetal acceleration decreases by a factor of 3.
E) The centripetal acceleration decreases by a factor of 9.
19. A car traveling at 20 m/s follows a curve in the road so that its centripetal acceleration is
5 m/s2. What is the radius of the curve?
A) 4 m
B) 8 m
C) 80 m
D) 160 m
E) 640 m
20. A 0.25-kg ball attached to a string is rotating in a horizontal circle of radius 0.5 m. If
the ball revolves twice every second, what is the tension in the string?
A) 2 N
B) 5 N
C) 7 N
D) 10 N
E) 20 N
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21. In an amusement park ride, a child stands against the wall of a cylindrical room that is
then made to rotate. The floor drops downward and the child remains pinned against
the wall. If the radius of the room is 2.15 m and the relevant coefficient of friction
between the child and the wall is 0.600, with what minimum speed is the child moving
if he is to remain pinned against the wall?
A) 7.26 m/s
B) 3.93 m/s
C) 12.1 m/s
D) 5.93 m/s
E) 9.80 m/s
22. Which force is responsible for holding a car in a frictionless banked curve?
A) the reaction force to the car's weight
B) the vertical component of the car's weight
C) the vertical component of the normal force
D) the horizontal component of the car's weight
E) the horizontal component of the normal force
23. Which force is responsible for holding a car in an unbanked curve?
A) the car's weight
B) the force of friction
C) the reaction force to the car's weight
D) the vertical component of the normal force
E) the horizontal component of the normal force
24. Determine the minimum angle at which a roadbed should be banked so that a car
traveling at 20.0 m/s can safely negotiate
the curve if the radius of the curve is 2.00 × 102 m.
A) 0.200°
B) 0.581°
C) 11.5°
D) 19.6°
E) 78.2°
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Use the following to answer question 25:
A 1800-kg Jeep travels along a straight 500-m portion of highway (from A to B) at a constant
speed of 10 m/s. At B, the Jeep encounters an unbanked curve of radius 50 m. The Jeep follows
the road from B to C traveling at a constant speed of 10 m/s while the direction of the Jeep
changes from east to south.
25. What is the magnitude of the frictional force between the tires and the road as the Jeep
negotiates the curve from B to C?
A) 9600 N
B) 7200 N
C) 3600 N
D) 1800 N
E) 1000 N
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Answer Key
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