Question

Assertion: A body can have acceleration even if its velocity is zero at a given instant of time.

Reason:  A body is momentarily at rest when it reverses its direction of motion.

 A) Both assertion and reason is true but the reason is the correct explanation of assertion.

 B) Both assertion and reason are true but the reason is not the correct explanation of assertion.

 C) Assertion is true but reason is false.

 D) Reason is true but the assertion is false.

Answer 1

Hint: Try to examine both assertion and reason and try to apply the concept of the laws of motion to answer this question. Try to answer this question by taking an example of a simple pendulum. Simple pendulum has two different positions that are extreme and mean. Try to analyse velocity and acceleration at these positions, you will get the answer.

Complete step by step answer:

We can answer this question from an example of a simple pendulum.

As the pendulum has some acceleration at extreme position but the velocity of the pendulum is zero. At the instant of the extreme position the direction of velocity gets reversed. Due to which we can say that acceleration of the pendulum is not zero. But the velocity of the pendulum is zero at the instant of the extreme position and the potential energy gets stored in the pendulum.

With this example we can also examine that when the velocity of the pendulum is getting reversed the pendulum has zero velocity at the extreme position.

Now read the assertion and reason both given in the question.

Assertion is correct as stated above with an example that a body can have acceleration even if its velocity is zero at a given instant of time. This is happening at the extreme position with the pendulum.

Reason is also correct as in the above example the pendulum is momentarily at rest when it reverses its direction of motion.

Therefore, the reason is the correct explanation of the assertion given as proved above with an example. So, option (A) is correct.

Note:

As discussed above about the laws of motion, I want to tell you that laws of motion are only applicable for the constant acceleration. For variable acceleration, these laws are not valid. As in the above example acceleration is constant but the velocity is changing continuously from zero to max and again zero. Try to find out the relation between all the three laws of motion.