Download Physics: Principle and Applications, 7e (Giancoli) Chapter 5 Circular

Physics: Principle and Applications, 7e (Giancoli)
Chapter 5 Circular Motion
5.1 Conceptual Questions
1) You are making a circular turn in your car on a horizontal road when you hit a big patch of ice, causing the
force of friction between the tires and the road to become zero. While the car is on the ice, it
A) moves along a straight-line path away from the center of the circle.
B) moves along a straight-line path toward the center of the circle.
C) continues to follow a circular path, but with a radius larger than the original radius.
D) moves along a path that is neither straight nor circular.
E) moves along a straight-line path in its original direction.
Answer: E
Var: 1
2) When a car goes around a circular curve on a horizontal road at constant speed, what force causes it to follow
the circular path?
A) the friction force from the road
B) the normal force from the road
C) gravity
D) No force causes the car to do this because the car is traveling at constant speed and therefore has no
acceleration.
Answer: A
Var: 1
3) A car goes around a circular curve on a horizontal road at constant speed. What is the direction of the friction
force on the car due to the road?
A) tangent to the curve in the forward direction
B) tangent to the curve opposite to the direction of the car's motion
C) perpendicular to the curve inward
D) perpendicular to the curve outward
E) There is no friction on the car because its speed is constant.
Answer: C
Var: 1
4) When an object moves in uniform circular motion, the direction of its acceleration is
A) in the same direction as its velocity vector.
B) in the opposite direction of its velocity vector.
C) is directed away from the center of its circular path.
D) is directed toward the center of its circular path.
E) depends on the speed of the object.
Answer: D
Var: 1
1
Copyright © 2014 Pearson Education, Inc.
5) If you swing a bucket of water fast enough in a vertical circle, at the highest point the water does not spill
out. This happens because an outward force balances the pull of gravity on the water.
A) True
B) False
Answer: B
Var: 1
6) When a car goes around a banked circular curve at the proper speed for the banking angle, what force cause it
to follow the circular path?
A) the friction force from the road
B) the normal force from the road
C) gravity
D) No force causes the car to do this because the car is traveling at constant speed and therefore has no
acceleration.
Answer: B
Var: 1
7) Two cars go around a banked curve at the proper speed for the banking angle. One car has tires with
excellent traction, while the other car has bald slippery tires. Which of these cars is more likely to slide on the
pavement as it goes around the curve?
A) the car with the new tires
B) the car with the bald tires
C) Neither car will slide.
D) It depends on if the pavement is wet or dry.
Answer: C
Var: 1
5.2 Problems
1) A particularly scary roller coaster contains a loop-the-loop in which the car and rider are completely upside
down. If the radius of the loop is 15.9 m with what minimum speed must the car traverse the loop so that the
rider does not fall out while upside down at the top? Assume the rider is not strapped to the car.
A) 11.4 m/s
B) 12.5 m/s
C) 10.1 m/s
D) 14.9 m/s
Answer: B
2) A 1000-kg car is moving at 30 m/s around a horizontal unbanked curve whose radius is 0.20 km. What is the
magnitude of the friction force required to keep the car from sliding?
A) 9000 N
B) 9800 N
C) 300 N
D) 900 N
E) 4500 N
Answer: E
Var: 1
3) The curved section of a horizontal highway is a circular unbanked arc of radius 740 m. If the coefficient of
static friction between this roadway and typical tires is 0.40, what would be the maximum safe driving speed for
2
Copyright © 2014 Pearson Education, Inc.
this horizontal curved section of highway?
A) 46 m/s
B) 48 m/s
C) 50 m/s
D) 52 m/s
E) 54 m/s
Answer: E
Var: 50+
4) A 250-kg motorcycle goes around an unbanked turn of radius 60.9 m at a steady 96.5 km/h. What is the
magnitude of the net force on the motorcycle?
A) 719 N
B) 2.95 × 103 N
C) 1.31 × 104 N
D) 4.31 × 104 N
Answer: B
Var: 1
5) A 2.0-kg toy is attached to the end of a 1.0-m very light string. The toy is whirled in a horizontal circular
path on a frictionless tabletop. If the maximum tension that the string can withstand without breaking is 350 N.
What is the maximum speed the mass can have without breaking the string?
A) 700 m/s
B) 26 m/s
C) 19 m/s
D) 13 m/s
Answer: D
Var: 1
6) A jet plane flying 600 m/s experiences an acceleration of 8.0 g when pulling out of a circular dive. What is
the radius of curvature of the circular part of the path in which the plane is flying?
A) 640 m
B) 4590 m
C) 7100 m
D) 9200 m
Answer: B
Var: 1
3
Copyright © 2014 Pearson Education, Inc.
7) One way that future space stations may create artificial gravity is by rotating the station. Consider a
cylindrical space station 380 m in diameter that is rotating about its longitudinal axis. Astronauts walk on the
inside surface of the space station. How long will it take for each rotation of the cylinder if it is to provide
"normal" gravity for the astronauts?
A) 39 s
B) 28 s
C) 6.2 s
D) 4.4 s
Answer: B
Var: 50+
8) A Ferris wheel has radius 10.0 m and makes one revolution every 8.0 s with uniform rotation. A person who
normally weighs 670 N is sitting on one of the benches attached at the rim of the wheel. What is the apparent
weight (the normal force exerted on her by the bench) of the person as she passes through the highest point of
her motion?
Answer: 420 N
Var: 1
9) LEAVE 9 BLANK.
10) A 1000-kg car is slowly picking up speed as it goes around a horizontal unbanked curve whose radius is 400
m. The coefficient of static friction between the tires and the road is 0.35. At what speed will the car begin to
skid sideways?
A) 9.3 m/s
B) 24 m/s
C) 37 m/s
D) 31 m/s
E) 19 m/s
Answer: C
Var: 1
11) A car moving at a steady 10 m/s on a level highway encounters a bump that has a circular cross-section with
a radius of 40 m. The car maintains its speed over the bump. What is the normal force exerted by the seat of the
car on a 60.0-kg passenger when the car is at the top of the bump?
A) 200 N
B) 390 N
C) 790 N
D) 440 N
E) 590 N
Answer: D
Var: 1
4
Copyright © 2014 Pearson Education, Inc.
12) A car moving at a steady 10 m/s on a level highway encounters a depression that has a circular cross-section
with a radius of 30 m. The car maintains its speed as it drives through the depression. What is the normal force
exerted by the seat of the car on a 60.0-kg passenger when the car is at the bottom of the depression?
A) 200 N
B) 390 N
C) 790 N
D) 490 N
E) 590 N
Answer: C
Var: 1
13) Pulling out of a dive, the pilot of an airplane guides his plane into a vertical circle with a radius of 600 m. At
the bottom of the dive, the speed of the airplane is 150 m/s. What is the apparent weight of the 70-kg pilot at
that point?
A) 3300 N
B) 690 N
C) 2600 N
D) 490 N
E) 1400 N
Answer: A
Var: 1
14) Pulling out of a dive, the pilot of an airplane guides his plane into a vertical circle. At the bottom of the
dive, the speed of the airplane is 300 m/s. What is the smallest radius allowable for the vertical circle if the
pilot's apparent weight is not to exceed 7.0 times his true weight?
A) 1700 m
B) 1530 m
C) 2200 m
D) 230 m
E) 42 m
Answer: B
Var: 1
15) In order to simulate weightlessness for astronauts in training, they are flown in a vertical circle. If the
passengers are to experience weightlessness, how fast should an airplane be moving at the top of a vertical
circle with a radius of 3.0 km?
A) 79 m/s
B) 170 m/s
C) 260 m/s
D) 310 m/s
E) 510 m/s
Answer: B
Var: 1
5
Copyright © 2014 Pearson Education, Inc.
16) In a carnival ride, passengers stand with their backs against the wall of a cylinder. The cylinder is set into
rotation and the floor is lowered away from the passengers, but they remain stuck against the wall of the
cylinder. For a cylinder with a 1.5 m radius, what is the minimum speed that the passengers can have so they do
not fall if the coefficient of static friction between the passengers and the wall is 0.25?
A) 8.9 m/s
B) 7.7 m/s
C) 3.0 m/s
D) 4.9 m/s
E) It depends on the mass of the passengers.
Answer: B
Var: 1
17) A 20-g bead is attached to a light 120-cm-long string as shown in the figure. This bead moves in a
horizontal circle with a constant speed of 1.5 m/s. What is the tension in the string if the angle α is measured to
be 11°?
A) 0.089 N
B) 0.041 N
C) 0.20 N
D) 0.22 N
E) 0.46 N
Answer: C
Var: 1
18) A 20-g bead is attached to a light 120 cm-long string as shown in the figure. If the angle α is measured to be
18°, what is the speed of the mass?
A) 0.55 m/s
B) 2.0 m/s
C) 3.8 m/s
D) 1.3 m/s
E) 1.1 m/s
Answer: E
Var: 1
6
Copyright © 2014 Pearson Education, Inc.
19) A small 175-g ball on the end of a light string is revolving uniformly on a frictionless surface in a horizontal
circle of diameter 1.0 m. The ball makes 2.0 revolutions every 1.0 s.
(a) What are the magnitude and direction of the acceleration of the ball?
(b) Find the tension in the string.
Answer: (a) 79.0 m/s2 toward the center of the circle (b) 13.8 N
Var: 1
20) A car traveling at a steady 20 m/s rounds an 80-m radius horizontal unbanked curve with the tires on the
verge of slipping. What is the maximum speed with which this car can round a second unbanked curve of radius
320 m if the coefficient of static friction between the car's tires and the road surface is the same in both cases?
A) 160 m/s
B) 80 m/s
C) 70 m/s
D) 40 m/s
E) 30 m/s
Answer: D
Var: 1
21) A future use of space stations may be to provide hospitals for severely burned persons. It is very painful for
a badly burned person on Earth to lie in bed. In a space station, the effect of gravity can be reduced or even
eliminated. How long should each rotation take for a doughnut-shaped hospital of 200-m radius so that persons
on the outer perimeter would experience 1/10 the normal gravity of Earth?
A) 91 min
B) 8.7 min
C) 4.6 min
D) 1.5 min
E) 0.011 min
Answer: D
Var: 1
22) A 600-kg car is going around a banked curve with a radius of 110 m at a steady speed of 24.5 m/s. What is
the appropriate banking angle so that the car stays on its path without the assistance of friction?
A) 29.1°
B) 13.5°
C) 33.8°
D) 56.2°
E) 60.9°
Answer: A
Var: 5
7
Copyright © 2014 Pearson Education, Inc.
23) The curved section of a speedway is a circular arc having a radius of 190 m. This curve is properly banked
for racecars moving at 34 m/s. At what angle with the horizontal is the curved part of the speedway banked?
A) 32°
B) 34°
C) 30°
D) 28°
E) 26°
Answer: A
Var: 50+
8
Copyright © 2014 Pearson Education, Inc.