Question

A car moving at a speed of $20m/s$ is slowed down to a speed of $10m/s$ over a distance of $30m$. What is the retardation produced during this time and what is the time taken?

• A. $5m/s^2$ and $5s$
• B. $4m/s^2$ and $2s$
• C. $5m/s^2$ and $2s$
• D. $4m/s^2$ and $5s$

Answer 1

The correct option is C $5m/s^2$ and $2s$

We have,
$u=20m/sv=10m/ss=30m$

We know:
$v^2=u^2+2as\Rightarrow 100=400+2\times a\times 30\Rightarrow a=-5m/s^2$
The negative sign indicates that the body is slowing down.
Also, $v=u+$ at $\Rightarrow 10=20-5t\Rightarrow t=2s$