Question

A body is thrown vertically upwards with initial velocity 9.8 m/s. It will remain in air for

• A. 1 sec
• B. 2 sec
• C. 3 sec
• D. 5 sec

Answer 1

Answer: (B)

2 sec

Given,

Take initial velocity $u=9.81m/s$

Acceleration is downward $a=-g=-9.81m/s^2$

When the body come to the ground, it has equal velocity in magnitude but opposite in direction.

Final velocity $v=-u$

Apply kinematic equation

$v=u+at$

$-u=u-gt$

$t=\frac{2u}{g}=\frac{2\times 9.81}{9.81}=2\sec$