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Chapter 13 - Forces

Multiple Choice
Identify the choice that best completes the statement or answers the question.

1.

If three balls of different materials were dropped at the same time from the same height, which would hit the ground first? (Assume there is no air resistance.)
 a. a tennis ball c. a solid steel ball b. a solid rubber ball d. They would all hit at the same time.

2.

Imagine that you are holding a 6 N book motionless in your hand. Which of the following is true?
 a. The book has a mass of 6 N. b. The total downward force on the book is 12 N. c. Your hand exerts an upward force of 6 N on the book. d. This situation illustrates unbalanced forces.

3.

Galileo proved that the rate at which an object falls
 a. increases with an increase in mass. c. is not affected by the mass. b. decreases with an increase in mass. d. increases with a decrease in mass.

4.

Air resistance is
 a. sliding friction. c. fluid friction. b. rolling friction. d. static friction.

5.

The amount of air resistance acting on an object depends on the object's
 a. size and shape. c. density and mass. b. mass and weight. d. None of the above

6.

An apple falls from a tree. The gravitational force on the apple is 1 N. If air resistance is 0.1 N, what is the net force on the apple?
 a. 0.1 N c. 1.0 N b. 0.9 N d. 1.1 N

7.

As long as the net force on a falling object is NOT zero, the object
 a. falls at a constant velocity. c. is pushed back up. b. accelerates downward. d. does not move.

8.

Astronauts float inside the space shuttle because they
 a. are massless. b. have no gravitational force acting on them. c. are in free fall. d. are weightless.

9.

The net force of unbalanced force pairs is ____.
 a. positive. c. either positive or negative. b. negative. d. zero.

10.

Orbiting objects appear to be weightless because they are
 a. in free fall. c. outside of Earth's atmosphere. b. weightless. d. in space.

11.

A satellite orbits Earth because
 a. it is caught in Earth's gravitational pull, like a tractor beam. b. it does not have enough fuel to start moving. c. it is moving forward while it is in free fall toward Earth. d. it is at rest.

12.

The KC-135 Vomit Comet is able to simulate an astronaut's apparent weightlessness in space by diving toward the ground at a 45° angle because
 a. it combines the motions of free fall with moving forward. b. gravitational force changes with angle. c. gravitational force depends on speed. d. gravitational force is zero when the distance changes quickly enough.

13.

Forces can be added together only if they are
 a. acting on the same object. b. balanced forces. c. unaffected by gravity. d. substantial.

14.

In physical science, a push or a pull is called a(n)
 a. force. b. acceleration. c. inertia. d. motion.

15.

What happens when two forces act in the same direction?
 a. They cancel each other out. b. The stronger one prevails. c. They add together. d. Their sum divided by two is the total force.

16.

Balanced forces acting on an object
 a. always change the object’s motion. b. sometimes change the object’s motion. c. never change the object’s motion. d. are not related to motion.

17.

The force that one surface exerts on another when the two rub against each other is called
 a. friction. b. acceleration. c. inertia. d. gravity.

18.

Which of the following is an example of rolling friction?
 a. your shoes on a sidewalk as you walk b. bike tires on the road as you ride c. a boat on the water as it sails d. two hands rubbing together

19.

The force of gravity on a person or object on the surface of a planet is called
 a. mass. b. air resistance. c. weight. d. free fall.

20.

The law of universal gravitation states that any two objects in the universe, without exception,
 a. attract each other. b. repel each other. c. combine to provide a balanced force. d. create friction.

21.

The amount of matter in an object is called its
 a. inertia. b. mass. c. force. d. balance.

22.

The force that pulls falling objects toward Earth is called
 a. gravity. b. free fall. c. acceleration. d. air resistance.

23.

When the only force acting on a falling object is gravity, the object is said to be
 a. stationary. b. decelerating. c. in free fall. d. a projectile.

24.

Air resistance is a type of
 a. motion. b. acceleration. c. velocity. d. friction.

25.

Objects falling through air experience a type of friction called
 a. terminal velocity. b. air resistance. c. inertia. d. rolling friction.

26.

Which type of elastic force is present in the strings on a guitar?
 a. compression b. tension c. friction d. inertia

27.

Which of the following examples demonstrates a compression force?
 a. plucking a guitar string b. pulling a wagon c. squeezing a sponge d. dropping an apple

28.

What holds up a large suspension bridge, such as the Golden Gate Bridge?
 a. the gravitational attraction between the bridge and its main supports b. fluid friction between the bridge’s supports and the water around them c. a lack of balance between the weight of the bridge and the supports below it d. an upward tension force in the cables that balances the weight of the bridge