Question

A ball is thrown vertically upward attains a maximum height of 45 m. The time after which velocity of the ball becomes equal to half the velocity of projection? (use g = 10 $m/s^2$)

• A. 2s
• B. 1.5 s
• C. 1 s
• D. 0.5 s

Answer 1

The correct option is B 1.5 s

Let the velocity of projection is $u$, and the final velocity at the top height will be zero.

The velocity of the projection is given as,

$v^2=u^2-2gh$

$u=\sqrt{2\times 10\times 45}$

$u=30m/s$

The time when the velocity of ball become to half velocity of projection is given as,

$v=u-gt$

$15=30-10\times t$

$t=1.5s$

Thus, the time when the velocity of ball become to half velocity of projection is $1.5s$.