Question

An object moving with a uniform velocity of $40m{s}^{-1}$ comes to rest in $10s$. What is the acceleration?

• A. $-4m{s}^{-2}$
• B. $4m{s}^{-2}$
• C. $-10m{s}^{-2}$
• D. $10m{s}^{-2}$

Answer 1

The correct option is A

$-4m{s}^{-2}$

Given, initial velocity $u=20m{s}^{-1}$, final velocity $v=0m{s}^{-1}$ and time $t=10s$.

Let acceleration be $a$.

As we know, $a=\frac{v-u}{t}$.

So, $a=\frac{0-40}{10}=-4m{s}^{-2}$.

Therefore, acceleration of the body is $-4m{s}^{-2}$ (The negative sign shows acceleration is against the direction of motion).