Question

A ball projected from ground vertically upward is at same height at time $t_{1}$ and $t_{2}$. The speed of projection of ball is [Neglect the effect of air resistance]

• A. $g\left[t_{2}-t_{1}\right]$
• B. $\frac{g\left[t_{1}+t_{2}\right]}{2}$
• C. $\frac{g\left[t_{2}-t_{1}\right]}{2}$
• D. $g\left[t_{1}+t_{2}\right]$

Answer 1

Answer: (B)

$t_{1}+t_{2}=$ total time of flight
$t_{1}+t_{2}=2 T$
$T=\frac{t_{1}+t_{2}}{2}$, also $T=\frac{u}{g}$
$\frac{u}{g}=\frac{t_{1}+t_{2}}{2}$
$\Rightarrow u=\frac{1}{2} g\left(t_{1}+t_{2}\right)$