Question

A projectile is thrown with velocity $v$ making an angle $\theta$ with the horizontal. It just crosses the top of two poles, each of height $h$, after $1$ second and $3$ second respectively. The time of flight of the projectile is

• A. $1s$
• B. $3s$
• C. $4s$
• D. $7.8s$

Answer 1

The correct option is C $4s$

When a projectile is in motion,
let the time to reach max height $=t_m$
And the body is at height '$h$' at $t_h$
$t_{h1}=t_m+\varphi$
$t_{h2}=t_m-\varphi$
Hence $t_m=\frac{(t_{h1}+t_{h2})}{2}=2s$
Time of flight = $2\times t_m=4s$
Hence option $C$ is correct.