Question

A body is projected at an angle${53}^0$ with velocity of 50 $m{s}^{-1}$. Calculate the time when velocity becomes 4/5 of initial velocity.

• A.
• B.
• C.
• D.

Answer 1

The correct option is A

$v_u=ucos\theta =50cos{30}^0=30m{s}^{-1}{v}_y=usin\theta -gt=40-10t\therefore v=\sqrt{v_x^2+v_y^2}=40{30}^2+{(40-10t)}^2={40}^2\Rightarrow t=4-\sqrt{7}s$