Question

A train is moving with a speed of $40m{s}^{-1}$. On applying brake, it comes to rest at 20 s, then the acceleration of the train is

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

Answer 1

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

Acceleration is defined as rate of change of velocity.
Given, the initial velocity, $u=40m{s}^{-1}$, final velocity, $v=0m{s}^{-1}$ and time taken, t = 20 s. Let the acceleration be 'a'.
Using the first equation of motion, v = u + at
$a=\frac{v-u}{t}=\frac{0-40}{20}=-2m{s}^{-2}$.
Therefore the acceleration of the train is $-2m{s}^{-2}$ (negative sign signifies deceleration i.e. there is a decrease in velocity).