A car traveling with velocity v is decelerated by a constant acceleration of magnitude a. It takes a time t to come to rest. If its initial velocity were doubled, the time required to stop would

A) double as well.

B) decrease by a factor of two.

C) stay the same.

D) quadruple.

E) decrease by a factor of four.

A stone is thrown straight up. When it reaches its highest point,

A) both its velocity and its acceleration are zero.

B) its velocity is zero and its acceleration is not zero.

C) its velocity is not zero and its acceleration is zero.

D) neither its velocity nor its acceleration is zero.

E) neither velocity nor acceleration can be determined without additional information.

Suppose a ball is thrown straight up, reaches a maximum height, then falls to its initial height. Make a statement about the direction of the velocity and acceleration as the ball is going up.

A) Both its velocity and its acceleration point upward.

B) Its velocity points upward and its acceleration points downward.

C) Its velocity points downward and its acceleration points upward.

D) Both its velocity and its acceleration points downward.

E) Neither velocity nor acceleration can be determined without additional information.

**EXPERT ANSWER**

A car traveling with velocity v is decelerated by a constant acceleration of magnitude a. It takes a time t to come to rest. If its initial velocity were doubled, the time required to stop would

A) double as well.

B) decrease by a factor of two.

C) stay the same.

D) quadruple.

E) decrease by a factor of four.

**Answer :**A) double as well.

A stone is thrown straight up. When it reaches its highest point,

A) both its velocity and its acceleration are zero.

B) its velocity is zero and its acceleration is not zero.

C) its velocity is not zero and its acceleration is zero.

D) neither its velocity nor its acceleration is zero.

E) neither velocity nor acceleration can be determined without additional information.

**Answer :**B) its velocity is zero and its acceleration is not zero.

Suppose a ball is thrown straight up, reaches a maximum height, then falls to its initial height. Make a statement about the direction of the velocity and acceleration as the ball is going up.

A) Both its velocity and its acceleration point upward.

B) Its velocity points upward and its acceleration points downward.

C) Its velocity points downward and its acceleration points upward.

D) Both its velocity and its acceleration points downward.

E) Neither velocity nor acceleration can be determined without additional information.

**Answer :**B) Its velocity points upward and its acceleration points downward.

**Answer : **C) twice as long.