Question

A rubber ball dropped from a certain height is an example of
A. Uniform acceleration
B. Uniform retardation
C. Uniform speed
D. None of these

Answer 1

Hint:
To answer this question, you need to understand why every object attracts towards the surface of the earth. It's obviously the gravitational force which acts on an object to pull it back to the surface.
Recall Newton’s law of gravitation to confirm why every object thrown upward falls back to the surface of the Earth.

Complete step by step answer:
The force of gravity acts on an object of mass m is given by the equation,
\[F = mg\]

Here, g is the acceleration due to gravity. Its value is constant and it is \[9.8\,m{s^{ - 2}}\].

Acceleration of the body moving with velocity v is given by the equation,
\[a = \dfrac{{dv}}{{dt}}\]

Here, \[\dfrac{{dv}}{{dt}}\] is the rate of change of velocity with respect to time t.

We need to check every option whether it is right or wrong.


Uniform acceleration.

Uniform acceleration means the acceleration of the rubber ball remains constant from its initial point to its final point. Since the acceleration due to gravity is the constant quantity, it does not change. Therefore, at any instant, the acceleration of the rubber ball remains constant.

The rubber ball will accelerate towards the ground with the uniform acceleration \[9.8\,m{s^{ - 2}}\].

Uniform retardation.

Uniform retardation means uniform decrease in the velocity of the object. The velocity of any object dropped from a certain height always increases. Therefore, the rubber ball will not undergo uniform retardation.

Uniform speed.

We know the first kinematic equation,
\[v = u + at\]

Here, v is the final velocity, u is the initial velocity, a is the acceleration and t is the time.

Since the acceleration of the rubber ball is not zero, the final velocity of the rubber ball is always greater than the initial velocity at any instant of time.

Therefore, the rubber ball will not undergo uniform speed.

So, the correct answer is “Option A”.

Note:
Acceleration due to gravity of any object is uniform irrespective of its mass. The falling object will never undergo retardation since the velocity of that object always increases with time.