Question

Assertion: In an elastic collision of two billiard balls, the total kinetic energy is conserved during the short time of oscillation of the balls (i.e., when they are in contact).
Reason: Energy spent against friction does not follow the law of conservation of energy.

• A. If both assertion and reason are true but the reason is the correct explanation of assertion.
• B. If both assertion and reason are true but the reason is not the correct explanation of assertion.
• C. If assertion is true but reason is false.
• D. If both the assertion and reason are false.
• E. If reason is true but assertion is false.

Answer 1

The correct option is D If both the assertion and reason are false.

First, let ius look at them as two independent statements.

During collision, there is deformity of shape of balls leading to increase in potential energy of the body, thus decreasing the kinetic energy momentarily.(Total energy remains constant, not KE) Thus, assertion is false.

Energy spent against friction should be considered when calculating total enery. Law of conservation of energy always applies, in every case. Only note is to identify the forms of energy. Reason is also false.