Question

A body starts from rest and moves with uniform acceleration for 2s. If then decelerates uniformly for 3s and stops. If deceleration is ${4ms}^{-2}$, the acceleration of the body is ____ ${ms}^{-2}$

• A. 10
• B. 8.7
• C. 4
• D. 6

Answer 1

The correct option is D 6

Given Final Velocity v=0, deceleration $a=4m{s}^{-2}$ and deceleration time $t=3s$,

Let $u$ be the velocity before the deceleration is started.

Using $v=u+at$ $\Rightarrow 0=u-4\times 3$ $\Rightarrow u=12,m{s}^{-1}$,

Now , During acceleration, Initial velocity $u_1$=0, time $t=2s$, Final velocity $u=12m{s}^{-1}$,

Let acceleration is $a$.

Using $v=u+at$ $\Rightarrow 12=0+a\times 2$ $\Rightarrow a=6m{s}^{-2}$