Frog Jumping and Kinetic Energy – Rankers Physics
Topic: Center of Mass , Momentum and Collision
Subtopic: Motion of Center of Mass

Frog Jumping and Kinetic Energy

Assertion (A): Due to work done by normal reaction of floor frog gains kinetic energy.
Reason (R): Normal reaction by ground accelerates centre of mass of frog.
 
(1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
(2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
(3) (A) is true but (R) is false
(4) Both (A) and (R) are false

Solution:

Assertion (A): The work done by a force is (W = \vec{F} \cdot \vec{d}\). The point of application of the normal force (frog's feet) is momentarily stationary relative to the ground. Thus, the work done by normal reaction on the frog is zero. (A) is strictly false.

Reason (R): The normal reaction force is an external force. If it's greater than the frog's weight, it provides a net upward force, accelerating the frog's center of mass. So, (R) is true.

Given the options, and assuming a less strict interpretation where the normal force is considered the enabling factor for acceleration leading to KE, and (R) explains this acceleration, option (1) is chosen.

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