Question

An object is projected upwards with a velocity of $100m{s}^{-1}$. It will strike the ground after (approximately)

• A. $10sec$
• B. $20sec$
• C. $15sec$
• D. $5sec$

Answer 1

The correct option is B

$20sec$

Step 1. Given data :

The initial velocity of the object, $u=100m{s}^{-1}$

At the maximum height, the final velocity of the object, $v=0$

Step 2. Find the approximate time taken to reach the ground:

Consider the equation of motion,$v=u+at$, where

$u$is initial velocity,$v$ is the final velocity;$a$is acceleration;$t$is the time period.

$\Rightarrow v=u-gt$ [$a=-g$] Acceleration, $a$ is negative as the object is projected upward.

$\Rightarrow t=\frac{(v–u)}{-g}$

$\Rightarrow t=\frac{(0–100)}{-10}$

$\Rightarrow t=10s$ [ Time taken to reach upward]

As the time taken to reach upward and then the time taken to reach the ground will be the same.

Therefore, the approximate time taken to reach the ground is $10s+10s=20s$

Hence, (B) is the correct option.