Question

Assertion: The velocity of a fall of a man jumping with a parachute first increases and then becomes constant.
Reason: The constant velocity of fall of man is called terminal velocity.
A. Assertion is true but the reason is false.
B. Assertion is false but the reason is true.
C. Both assertion and reason are true but reason is not the correct explanation of assertion.
D. Both assertion and reason are true and reason is the correct explanation of assertion.

Answer 1

Hint:The maximum velocity that a body attains when in a free fall or in a liquid. This happens due to the resistive forces of the air and liquid respectively. The resistive force of the air is often termed as air drag and the resistive force of a liquid is termed as viscosity of that particular liquid. Terminal velocity is attained when resistance forces and gravitational force become equal.

Complete step by step answer:
When a man initially falls from a height it is acted upon by the gravitational force due to the earth which is equal to the weight $W = mg$ where m is the mass of the person and g is the acceleration due to gravity.

When the resistive force becomes equal to the weight of the person the body stops to accelerate as there are no other forces acting on it. So it starts to move with a constant velocity and we term this velocity as terminal velocity. It is represented by ${V_T}$. So both assertion and reason are correct and reason is the correct explanation of assertion.

Therefore, option D is correct.

Note:The terminal velocity can be visualized by dropping a coin in water. For this first take a transparent glass and fill it with water. Now drop a coin in the water. You will notice that the coin will initially fall with an acceleration and you will see that the velocity of the coin will increase initially and slowly you will notice that it becomes constant when it reaches the end.