Question

A ball has been thrown vertically up such that distance covered by it in $4th$ and $6th$ second is same. If $g=10m/s^2$, the initial speed of the ball is

• A. $45m/s$
• B. $25m/s$
• C. $50m/s$
• D. $10m/s$

Answer 1

Answer: (C)

$50m/s$

When it travel $s$ distance from ground.

$\Rightarrow t=4s$

Now when it reaches the same height from the ground $t=6s$

$S=ut-\frac{1}{2}g{t}^2$

Where $u=$ Initial speed.

$S=$ Distance traveled.

$S=ut-5t^2$

at $t=4s$

$S=4u-80$

$\therefore 4u-S=80⟶\left(i\right)$

and, at $t=6s$

$S=6u-180$

$6u-S=180⟶\left(ii\right)$

Subtract $\left(i\right)$ From $\left(ii\right)$

$2u=100$

$u=50m/s$