Question

A body moving along a straight line at $20\mathrm{m}/\mathrm{s}$ undergoes an acceleration of $-4\mathrm{m}/{\mathrm{s}}^2$. After two seconds its speed will be-

• A. $-8\mathrm{m}/\mathrm{s}$
• B. $12\mathrm{m}/\mathrm{s}$
• C. $16\mathrm{m}/\mathrm{s}$
• D. $28\mathrm{m}/\mathrm{s}$

Answer 1

The correct option is B

$12\mathrm{m}/\mathrm{s}$

Step 1: Given

As per the data given,

Initial velocity, $\mathrm{u}=20\mathrm{m}/\mathrm{s}$

Acceleration due to gravity $a=-4m/s^2$

Time, $t=2s$

Final velocity $v=?$

Step 2: Calculating the final velocity of the body

We know that, according to the first equation of motion,
$\mathrm{v}=\mathrm{u}+\mathrm{at}$

Here v is final velocity and u is initial velocity and t is time.

$v=20+(-4\times 2)$

$v=20-8=12\mathrm{m}/\mathrm{s}$

Thus, the final velocity of the body is $12m/s$.

Hence, option B is the correct answer.