2.1.5 Acceleration

Question 1

note

Answer 1

• In many physical situations, the change in velocity per unit time or the average acceleration is important: . For example, if the limousine’s velocity changes from 100 mph to 0 mph in 2 min, the limousine has stopped at a stop sign.If the limousine’s velocity changes from 100 mph to 0 mph in just 0.5 s, the limousine has been in an accident.
• The acceleration at an instant in time is found by calculating the average acceleration over a diminishingly small time interval. The instantaneous acceleration is and its unit is . The first derivative of position with respect to time is velocity. The first derivative of velocity with respect to time is acceleration.The sign of acceleration may be somewhat counter-intuitive at first. In the first example, the iguanodon accelerates to the right, or in the positive direction.
• In the second example, he slows down as he moves in the negative x-direction. In this case his acceleration is in the positive direction since the change in his velocity is positive. In the third example, the iguanodon slows down as he moves in the positive x-direction. His acceleration is negative because the change in his velocity is negative

Question 2

Which of the following statements concerning velocity and acceleration is not correct?

Answer 2

If a vehicle speeds up, its acceleration cannot decrease.

Question 3

The graph illustrates the motion of an object. Which of the following statements describes the acceleration of the object?

Answer 3

The acceleration is constant.

Question 4

What is the average acceleration of an object that speeds up from 32 mph to 79 mph in 6 seconds?

Answer 4

0.0022 mi / s2

Question 5

The graph illustrates the motion of an object. Which of the following statements is correct?

Answer 5

The acceleration of the object increases with time.

Question 6

The diagram shows two trains traveling in opposite directions on a track. Suppose that Train A starts at rest at x = 0 and moves very quickly to the left for a period of 5 minutes. At 5 minutes, Train A instantly stops. Train B also starts at x = 0 and moves at a constantly increasing velocity to the right. At 5 minutes, Train B is continuing to move at a constantly increasing velocity. Which of the following statements correctly describes Δv and the average acceleration for each train?

Answer 6

Train A:
Δv is zero
average acceleration is zero
Train B:
Δv is positive
average acceleration is positive

Question 7

Which of the following regarding average acceleration is correct?

Answer 7

The ratio of the change in velocity to the change in time is equivalent to the acceleration.

Question 8

Consider the motion of a train. Which of the following is correct? Assume that the positive direction is to the right.

Answer 8

None of these are correct.

Question 9

Which of the following best defines average acceleration?

Answer 9

The change in velocity over a given time interval.

Question 10

The symbol Δ is used to denote change. Which of the following is the correct, general convention for this symbol?

Answer 10

The term Δ means final (something) − initial (something).