Download 3) An object moves in a circular path at a constant speed

Review questions for Chapter 5 Exam
Honors Physics
1) An object moves in a circular path at a constant speed. Compare the direction of the object's velocity and
acceleration vectors.
A) Both vectors point in the same direction.
B) The vectors point in opposite directions.
C) The vectors are perpendicular.
D) The question is meaningless, since the acceleration is zero.
Answer: C
2) When an object experiences uniform circular motion, the direction of the net force is
A) in the same direction as the motion of the object.
B) in the opposite direction of the motion of the object.
C) is directed toward the center of the circular path.
D) is directed away from the center of the circular path.
Answer: C
3) A roller coaster car (mass = M) is on a track that forms a circular loop (radius = r) in the vertical plane. If the car
is to just maintain contact with the track at the top of the loop, what is the minimum value for its speed at that point?
A) rg
B) (rg)1/2
C) (2rg)1/2
D) (0.5rg)1/2
Answer: B
4) A car goes around a curve of radius r at a constant speed v. Then it goes around the same curve at half of the
original speed. What is the centripetal force on the car as it goes around the curve for the second time, compared to
the first time?
A) twice as big
B) four times as big
C) half as big
D) one-fourth as big
Answer: D
5) A car goes around a curve of radius r at a constant speed v. Then it goes around a curve of radius 2r at speed 2v.
What is the centripetal force on the car as it goes around the second curve, compared to the first?
A) four times as big
B) twice as big
C) one-half as big
D) one-fourth as big
Answer: B
6) The gravitational force between two objects is proportional to
A) the distance between the two objects.
B) the square of the distance between the two objects.
C) the product of the two objects.
D) the square of the product of the two objects.
Answer: C
7) The gravitational force between two objects is inversely proportional to
A) the distance between the two objects.
B) the square of the distance between the two objects.
C) the product of the two objects.
D) the square of the product of the two objects.
Answer: B
8) Two objects attract each other gravitationally. If the distance between their centers is cut in half, the
gravitational force
A) is cut to one fourth.
B) is cut in half.
C) doubles.
D) quadruples
Answer: D
9) Two objects, with masses m1 and m2, are originally a distance r apart. The magnitude of the gravitational force
between them is F. The masses are changed to 2m1 and 2m2, and the distance is changed to 5r. What is the
magnitude of the new gravitational force?
A) F/25
B) F/5
C) (4/25)F
D) 5F
Answer: C
10) The acceleration of gravity on the Moon is one-sixth what it is on Earth. An object of mass 72 kg is taken to the
Moon. What is its mass there?
A) 12 kg
B) 72 kg
C) 72 N
D) 12 N
Answer: B
11) A hypothetical planet has a mass of half that of the Earth and a radius of twice that of the Earth. What is the
acceleration due to gravity on the planet in terms of g, the acceleration due to gravity at the Earth?
A) g
B) g/2
C) g/4
D) g/8
Answer: D
12) The acceleration of gravity on the Moon is one-sixth what it is on Earth. The radius of the Moon is one-fourth
that of the Earth. What is the Moon's mass compared to the Earth's?
A) 1/6
B) 1/16
C) 1/24
D) 1/96
Answer: D
13) The average distance from the Earth to the Sun is defined as one "astronomical unit" (AU). An asteroid orbits
the Sun in one-third of a year. What is the asteroid's average distance from the Sun?
A) 0.19 AU
B) 0.48 AU
C) 2.1 AU
D) 5.2 AU
Answer: B
14) How many revolutions per minute must a circular, rotating space station of radius 1000 m rotate to produce an
artificial gravity of 9.80 m/s2?
A) 0.65 rpm
B) 0.75 rpm
C) 0.85 rpm
D) 0.95 rpm
Answer: D
15) A 0.50-kg mass is attached to the end of a 1.0-m string. The system is whirled in a horizontal circular path. If
the maximum tension that the string can withstand is 350 N. What is the maximum speed of the mass if the string is
not to break?
A) 700 m/s
B) 26 m/s
C) 19 m/s
D) 13 m/s
Answer: B
16) A stone, of mass m, is attached to a strong string and whirled in a vertical circle of radius r. At the exact top of
the path the tension in the string is 3 times the stone's weight. The stone's speed at this point is given by
A) 2(gr)1/2.
B) (2gr)1/2.
C) (gr)1/2.
D) 2gr.
Answer: A
17) A stone, of mass m, is attached to a strong string and whirled in a vertical circle of radius r. At the exact bottom
of the path the tension in the string is 3 times the stone's weight. The stone's speed at this point is given by
A) 2(gr)1/2.
B) (2gr)1/2.
C) (gr)1/2.
D) 2gr.
Answer: B
18) A pilot makes an outside vertical loop (in which the center of the loop is beneath him) of radius 3200 m. At the
top of his loop he is pushing down on his seat with only one-half of his normal weight. How fast is he going?
A) 5.0 m/s
B) 25 m/s
C) 125 m/s
D) 625 m/s
Answer: C
19) The maximum force a pilot can stand is about seven times his weight. What is the minimum radius of curvature
that a jet plane's pilot, pulling out of a vertical dive, can tolerate at a speed of 250 m/s?
A) 4.25 m
B) 3.64 m
C) 1060 m
D) 911 m
Answer: C
20) A car goes around a flat curve of radius 50 m at a speed of 14 m/s. What must be the minimum coefficient of
friction between the tires and the road for the car to make the turn?
A) 0.20
B) 0.40
C) 0.60
D) 0.80
Answer: B
21) A 175-kg ball on the end of a string is revolving uniformly in a horizontal circle of radius 0.500 m. The ball
makes 2.00 revolutions in a second.
(a) Determine the speed of the ball.
(b) Determine the ball's centripetal acceleration.
(c) Determine the force a person must exert on opposite end of the string.
Answer: (a) 6.28 m/s
(b) 79.0 m/s2
(c) 13.8 N
22) The mass of the Moon is 7.4 × 1022 kg and its mean radius is 1.75 × 103 km. What is the acceleration due to
gravity at the surface of the Moon?
A) 2.8 × 106 m/s2
B) 9.80 m/s2
C) 1.6 m/s2
D) 0.80 m/s2
Answer: C
23) An astronaut goes out for a "space-walk" at a distance above the Earth equal to the radius of the Earth. What is
her acceleration due to gravity?
A) zero
B) g
C) g/2
D) g/4
Answer: D
24) The radius of the Earth is R. At what distance above the Earth's surface will the acceleration of gravity be 4.9
m/s2?
A) 0.41 R
B) 0.50 R
C) 1.00 R
D) 1.41 R
Answer: A
25) An object weighs 432 N on the surface of the Earth. The Earth has radius r. If the object is raised to a height of
3r above the Earth's surface, what is its weight?
A) 432 N
B) 48 N
C) 27 N
D) 0 N
Answer: C
26) A satellite is in a low circular orbit about the Earth (i.e., it just skims the surface of the Earth). What is the
speed of the satellite? (The mean radius of the Earth is 6.38 × 10 6 m.)
A) 5.9 km/s
B) 6.9 km/s
C) 7.9 km/s
D) 8.9 km/s
Answer: C
27 A satellite is in a low circular orbit about the Earth (i.e., it just skims the surface of the Earth). How long does it
take to make one revolution around the Earth? (The mean radius of the Earth is 6.38 × 10 6 m.)
A) 81 min
B) 85 min
C) 89 min
D) 93 min
Answer: B
28) Europa, a moon of Jupiter, has an orbital diameter of 1.34 × 10 9 m, and a period of 3.55 days. What is the mass
of Jupiter?
A) 1.83 × 1027 kg
B) 1.85 × 1027 kg
C) 1.87 × 1027 kg
D) 1.89 × 1027 kg
Answer: D
29) The planet Jupiter is 7.78 × 1011 m from the Sun. How long does it take for Jupiter to orbit once about the
Sun? (The distance from the Earth to the Sun is 1.50 × 10 11 m.)
A) 1 yr
B) 3 yr
C) 6 yr
D) 12 yr
Answer: D
Diff: 2
Type: BI
Var: 1
Page Ref: Sec. 5.9
30) It takes the planet Jupiter 12 years to orbit the Sun once. What is the average distance from Jupiter to the Sun?
(The distance from the Earth to the Sun is 1.5 × 10 11 m.)
A) 3.9 × 1011 m
B) 5.2 × 1011 m
C) 7.9 × 1011 m
D) 9.7 × 1011 m
Answer: C