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If the displacement of a body is proportional to the square of time, then the body is moving with
A. Uniform acceleration
B. Increasing acceleration
C. Decreasing acceleration
D. Uniform velocity

Answer
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Hint:Write the equation for the displacement of the body as a function of time. Then differentiate the displacement with respect to time and find the velocity. After this, differentiate the velocity with respect to time to find the acceleration.

Formula used:
v=dxdt
a=dvdt

Complete step by step answer:
It is given that the displacement of a body is proportional to the square of time.

Therefore, we can write that xt2 …. (i),
where x is the displacement of the body and t is time.

This means that if the time is increased by factor ‘n’ then the displacement of the particle will increase by a factor of n2.

By adding a proportionality constant k to (i), we can write an equation for x as x=kt2 ….. (ii).

We can see that the options are stating about the velocity and the acceleration of a body.
Velocity (v) of a body is the first derivative of displacement with respect to time.

Therefore, differentiate (ii) with respect to time t.
v=dxdt=ddt(kt2)v=dxdt=ddt(kt2)
v=2kt …. (iii)

Now, we can see that the velocity of the given body is directly proportional to t.
Acceleration (a) of a body is the first derivative of its velocity with respect to time t.

Therefore, differentiate (iii) with respect to time t.
a=dvdt=ddt(2kt)
a=2k.

We know that k is a constant. Therefore, the acceleration of the body is constant.
Constant acceleration is also called uniform acceleration.

Hence, the correct option is A.

Note:If you are well known with the kinematic equations for uniform acceleration, then this would be a very easy problem.

One of the kinematic equations say that x=ut+12at2, where u is the initial velocity of the body.

If we put a condition that the body was at rest initially ( u=0), then the displacement of the body is equal to x=12at2.
xt2.

Hence, the body is travelling with uniform acceleration.