Question

A train is moving with a speed of $60m{s}^{-1}$. On applying the brakes, it comes to rest in $20s$. What is the magnitude of average acceleration (deceleration) of the train?

• A. $2m{s}^{-2}$
• B. $3m{s}^{-2}$
• C. $4m{s}^{-2}$
• D. $5m{s}^{-2}$

Answer 1

The correct option is B $3m{s}^{-2}$

Given:
Initial velocity: $u=60m{s}^{-1}$
Final velocity: $v=0m{s}^{-1}$ (train is coming to rest)
Time taken: $t=20s$.
Let the average acceleration be $a$

Acceleration is defined as the rate of change of velocity.
$a=\frac{v-u}{t}$
$a=\frac{0-60}{20}=-3m{s}^{-2}$ (negative sign shows that the train is decelerating)