Question

A body is projected vertically upward with an initial velocity u. If acceleration due to gravity is g , the time for which it remains in air, is : *

u/g

ug

2u/g

u/2g​

Answer 1

Given:

A body is projected vertically upward with an initial velocity u. Acceleration due ti gravity is g.

To find:

Time for which it remains in air ?

Calculation:

• First of all , when the object is thrown vertically upwards, it will reach a maximum height then come downwards and reach the ground.

• So, the net displacement in this journey will be zero.

Applying EQUATIONS OF KINEMATICS:

$h = ut + \dfrac{1}{2} a {t}^{2}$

• So, value of 'h' will be zero as described above.

$\implies 0 = ut + \dfrac{1}{2} ( - g) {t}^{2}$

$\implies \: \dfrac{1}{2} g {t}^{2} = ut$

$\implies \: t = \dfrac{2u}{g}$

So, the time in air will be 2u/g.