Question

Which of the following statements is not correct?

• A. The zero velocity of a body at any instant does not necessarily imply zero acceleration at that instant
• B. The Kinematic equation of motions are true only for motion in which the magnitude and the direction of acceleration are constants during the course of motion
• C. The sign of acceleration tells us whether the particle’s speed is increasing or decreasing
• D. All of these

Answer 1

Answer: (C)

The sign of acceleration tells us whether the particle’s speed is increasing or decreasing

Answer 2

The sing of accelerations does not tell us whether the particle’s speed is increasing or decreasing. The sing of accelerations depends on the choice of the positive directions of the axis. For example, if the vertically upward directions is chosen to be positive directions of the axis, the accelerations due to gravity is negative. If a particle is falling under gravity, this acceleration though negative results in increase in speed.