Chapter 1 Test Problems

How Things Work (Bloomfield) Chapter 1 Test Problems

Section 1.1 – Skating

• Suppose you have two cars, and the larger one is twice as massive as the smaller one.

If you and a friend push on them so that their accelerations are equal, how must the forces applied to the cars compare?

• The force on the larger car is equal to that on the smaller car
• The force on the larger car is ½ that on the smaller car.
• The force on the larger car is twice that on the smaller car.
• The force on the larger car is more than three times that on the smaller car.

ANS: C DIFF: E

• Which of the following devices on a car can be used to cause the car to accelerate?
• The gas pedal
• The brake pedal
• The steering wheel
• All the above

ANS: D DIFF: E

• The acceleration of an object is equal to
• the rate of change of its position
• the rate of change of its velocity
• the rate of change of its speed only
• the time an object has been in motion

ANS: B DIFF: E

• Suppose you are at a stop light and realize that an important antique physics textbook

sale ends in five minutes. Naturally, you start off very rapidly. To you, some papers on the dashboard fly straight backwards. To an observer on the ground they

• remained where they were.
• moved forward rapidly.
• moved backwards rapidly.
• fell straight down.

ANS: A DIFF: E

• The SI units of acceleration are
• m/s
• kgm/s

2

• m/s

2

• kg m

2 /s 2

ANS: C DIFF: E

(How Things Work The Physics of Everyday Life 5e Louis A. Bloomfield) (Test Bank all Chapters) 1 / 4

• Suppose you have a car traveling down the road at constant speed and not changing

direction. It is experiencing gravity, wind resistance and frictional forces from the road.What can be said about the car’s acceleration?

• It is accelerating because there are forces acting on it.
• It accelerating because the motor is running, propelling the car forward.
• It is not accelerating because gravity holds it down.
• It is not accelerating because it has constant velocity.

ANS: D DIFF: M

• Suppose you are driving north and suddenly hit your brakes to avoid a dog in the road.

As you come to a stop your acceleration is directed

• North
• South
• Nowhere because acceleration is a scalar
• Downwards

ANS: B DIFF: M

• If you are backing up but slowing down, your acceleration is directed
• backwards
• nowhere
• forwards
• to the left

ANS: C DIFF: M

• Under what conditions are the values of average speed and the magnitude of the

average velocity equal?

• When moving in a straight line
• When moving in a straight line and not turning around
• When moving in a circular path
• When walking around the perimeter of a rectangle

ANS: B DIFF: M

• You are making a round trip from City A to City B and back to City A again at

constant speed. At what point in the trip is your average speed equal to three times the magnitude of your average velocity?

ANS: Since velocity = change in position divided by time interval and average

speed = total distance divided by time interval we need to find a point in the trip where the distance traveled is equal to three times the object’s change in position. Here it is useful to break the trip into four equal parts. We can see that halfway between the two cities on the way back to city A, three parts distance have been covered but the difference in position is only one part. Hence it is at the midway point on the return where the average speed is three times the average velocity.

DIFF: H

• A frequent flyer is suing an airline. She claims that during landing, the plane’s rapid

acceleration caused a suitcase on a luggage rack in front of her to fly backwards and hit 2 / 4

her. Using any of Newton’s laws of motion, please support or refute the passenger’s claim.

ANS: Here I would use Newton’s first law of motion. The plane is accelerating

backwards when landing. The book indeed has inertia, so Newton’s first law suggests that the book would tend to remain in a constant state of motion, so it would tend to slip forward (relative to the plane), not backward. Hence the passenger’s claim is refuted.

DIFF: M

• A friend states Newton’s First Law of Motion as “An object will move in a straight

line unless acted upon by a force” Please evaluate the scientific merit of his statement.

ANS: the friend is almost right but has left out some very important loopholes.

First off, it is a non-zero net force that causes acceleration, not necessarily any lone force.Also, a non-zero net force will make an object accelerate, meaning it will speed up, slow down or curve – not just curve as the friend suggests. The object could accelerate in a straight line.

DIFF: H

• You walk in a given direction for 20 m during the first 5 seconds of a trip and then

15 m during the next 2 seconds. Your average speed is equal to

• 8 m/s
• 2 m/s
• 5 m/s
• –5 m/s

ANS: C DIFF: M

• To cause a 25 kg object to experience an acceleration of 2 m/s

2 the net force that needs to be applied to the object is

A) 10 N

B) 5 N

C) 50 N

D) 100 N

ANS: C DIFF: E

• A net force of 8 N is applied to a 2 kg object. The object’s acceleration is
• 4 m/s

2

• 8 m/s

2

• 16 m/s

2

• 2 m/s

2

ANS: A DIFF: E

• An object experiences a net force of 20 N and has an acceleration of 4 m/s

2 . The object’s mass must be

• 20 kg
• 5 kg
• 80 kg
• 2 kg 3 / 4

ANS: B DIFF: E

• At a speed of 12 m/sec how far can you travel in one minute?

A)12 m

• 72 m
• 60 m
• 720 m

ANS: D DIFF: E

• Consider a 6 kg box of holiday candy on a horizontal surface such as a table. There is

a 10N applied force to the right and a 7 N frictional force to the left. Suppose the block moves 3 m to the right across the table, to its impending doom of hungry guests.

• Please calculate the work done by the 10 N force.

ANS: W = Fd = (10)(3) = 30J

• What is the work done by the 7 N frictional force?

ANS: W = Fd = (-7)(3) = -21J

DIFF: H

• Is it possible for the magnitude of an object’s average velocity to be greater than its

average speed? How about average speed being greater than the magnitude of the average velocity? Please explain.

ANS: The magnitude of the average velocity for an object may be less than its

average speed but not the other way around. One can look at the definition of the two quantities involved for an explanation. Average speed is distance divided by time and average velocity is displacement (finishing position minus initial position) divided by time. Since the time intervals are the same for both quantities the question boils down to comparing net displacement to distance traveled. If an object changes direction the difference in its position will be less than the distance traveled but under no circumstances can the finishing point minus starting point ever be greater than the distance traveled.

DIFF: M

• Suppose an ice skater is moving on the surface of a frozen lake at constant velocity.

What is true about the external (outside) forces acting on the skater?

• There are none.
• There could be some but they all cancel out.
• Gravity can be ignored.
• The all are perfectly horizontal.

ANS: B DIFF: E

• The value of the average velocity for any round trip is equal to
• Total distance traveled divided by total trip time.
• The final acceleration multiplied by trip time
• Zero.
• The person’s speed halfway through the path.
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