Question

Which of the following has zero acceleration?

Answer 1

'Acceleration' means any change in speed or direction
of motion.

so
 C).  No acceleration.  Straight, at constant speed. 
No change of speed or direction.

Answer 2

Answer:

C. A person running 100 m straight across a field at a constant speed.

Explanation:

Acceleration is defined as the change in the velocity per unit time. Velocity have both direction and magnitude (speed) . So, acceleration involves both change in direction and speed.

A).  The satellite is in a curved orbit, so direction of satellite is constantly changing. Hence, not the answer.

B). The car is following a curve, so its direction is changing. Hence, not the answer.

C). The person is running straight at constant speed which means no change of speed or direction. Hence, it is the answer.

D). The person is on curved track, so his/her direction is changing. Hence, not the answer.