Question

Which one of the following statements is correct?

• A. If the net external force on body is zero, then velocity of center of mass is zero.
• B. Acceleration of a projectile is maximum at the highest point.
• C. A body can be at rest or in motion at the same time depending upon frame.
• D. A particle having constant speed can have acceleration.

Answer 1

The correct option is C A body can be at rest or in motion at the same time depending upon frame.

a. Zero net force means zero acceleration; velocity can be constant.
b. Acceleration is constant throughout the projectile.
c. e.g. A person sitting in a moving car is at rest w.r.t. the car but in motion w.r.t the ground.
d. Acceleration is rate of change of speed.