Answer the following questions.

1. The speed of an accelerated body changes with time.

A. True

B. False

2. The position of a body in motion changes with time.

A. True

B. False

3. The velocity of an accelerated body changes with time.

A. True

B. False

4. The words motion and acceleration can be used interchangeably.

A. True

B. False

5. The acceleration of a body with zero speed is zero.

A. True

B. False

1. B 2. A. 3. A. 4. B 5. B

Explanation:

1) The statement is false, because the acceleration (by definition) is the rate of change of velocity, which is a vector.

As a vector, it can change the magnitude, the direction, or both. As the speed is only the magnitudde, there can be an acceleration at constant speed, as in an uniform circular movement, where the acceleration produces a change in direction, not in the speed.

2) If the body is in motion (assuming that it is only translational motion) the position (displacement from the origin) must be change with time, so the statement is true.

3) This is true, as the acceleration, as we said above, is the rate of change of the velocity vector.

4) The statement is false, as an object moving at constant speed along a straight line is in movement, and is not accelerated at all.

5) The statement is false, as a body can momentarily come to an stop (before changing direction, for instance), and be accelerated at the same time.

The best example is an object thrown up in the air: once released, the only force acting on it is gravity, which produces an acceleration in opposite direction to the initial speed, until it causes the object to stop, change direction, and finally fall freely.