Question

A ball is thrown directly upward and experiences no air resistance. Which one of the following
statements about its motion is correct?
A) The acceleration of the ball is upward while it is traveling up and downward while it is
traveling down.
B) The acceleration of the ball is downward while it is traveling up and upward while it is
traveling down.
C) The acceleration is downward during the entire time the ball is in the air.
D) The acceleration of the ball is downward while it is traveling up and downward while it
is traveling down but is zero at the highest point when the ball stops.

Answer 1

Answer:

C) The acceleration is downward during the entire time the ball is in the air.

Explanation:

If we neglect air resistance, there is only one force acting on the ball, which is the force of gravity.

The magnitude of the force of gravity is

F = mg

where m is the mass of the ball and g is the acceleration of gravity. According to Newton's second law, therefore the acceleration of the ball during the entire motion is

$a=\frac{F}{m}=\frac{mg}{m}=g$

So, it is equal to the acceleration of gravity ($9.8 m/s^2$) and in the same direction (downward). Since this force is constant, then the acceleration is the same during the entire motion, therefore the correct answer is

C) The acceleration is downward during the entire time the ball is in the air.