Question

An object is thrown vertically upward with a velocity of $10m{s}^{-1}$. It strikes the ground after _______ seconds. (Take $g=10m{s}^{-2}$)

• A. 10
• B. 2
• C. 5
• D. 1

Answer 1

The correct option is B 2

Given:

Initial velocity $u=10m/s$

Gravitational acceleration $g=10m/s^2$

$\text{Time to ascend maximum height}$:

When the object is ascending, $g$ is causing deceleration. At the maximum height, the velocity of the object is zero.

Let $t_1$ is the time required to reach the maximum height.

Thus, using the equation $v=u-gt$ we get,

$0=10-(10\times t_1)$

$\Rightarrow t_1=1sec$

$\text{Time required to reach the maximum height}=\text{Time required to fall down to the ground from the maximum height}$

Thus, the total time required is $(1+1)=2sec$