Question

When does instantaneous speed equal average speed?
A. In an accelerated motion
B. In a de-accelerated motion
C. In a uniform motion with zero acceleration
D. Never

Answer 1

Hint:In order to answer this question, first we have to define instantaneous speed then average speed and after comparing these definitions we can approach the solution of this question.

Complete step by step answer:
Instantaneous speed is defined as the speed of a body at any instant of time. Suppose a body is moving, it starts its motion from time, t=0. Suppose if we want to know the speed of the body at a time, t=5s then this speed will be termed as instantaneous speed.
On the other hand, the average speed of a body is defined as the ratio of the total distance covered by the body to the total time taken by it to cover that distance. Now if a body is moving with constant speed say with a speed of 5m/s then if, at time t=3s, its instantaneous speed will be 5m/s and for average speed, we first calculate the total distance which comes out to be 15 m and divide it by total time that is 3 s then average speed comes out to be 5m/s. Now if we want to see at t=5s, then instantaneous speed is 5m/s and for average speed again we calculate total distance which comes out to be 25m and divide it by total time that is 5s, then average speed comes out to be 5m/s. The correct option is (C).

Note: Remember that when a body moves with constant speed then its acceleration is zero and sometimes you may get confused about these two terms as it looks similar so keep special attention on it.