Question

A particle is thrown with a velocity of $um/s$. It passes $A$ and $B$ as shown in the figure at time $t_1=1s$ and $t_2=3s$. The value of $u$ is
$(g=10m/s^2)$

• A. $20m/s$
• B. $10m/s$
• C. $40m/s$
• D. $5m/s$

Answer 1

The correct option is C $40m/s$

We know that
Time of ascent of a projectile = Time of descent of a projectile
As both $A$ and $B$ are at same height, so we can say
$t_1+t_2=T$ (time of flight)
$\Rightarrow T=1+3$
$\frac{2u\sin \theta }{g}=4$
$u\sin {30}^{\circ }=20$
$\Rightarrow u=40m{s}^{-1}$
Hence, the correct answer is option (c)