A ball is thrown upwards, it takes 4 sec to reach back to the ground. Find its initial velocity:

Question

A ball is thrown upwards, it takes 4 sec to reach back to the ground. Find its initial velocity: (A)  30 ms-1  (B)  10 ms-1  (C)  40 ms-1  (D)  20 ms-1

Tardigrade Admin · Accepted Answer

Since the ball is thrown upwards and it reaches back,
so time to reach maximum height is half of total time i.e.,

t_{maximum} = 2 sec

Also speed at maximum height is zero, so

o = u - g t_{m a x}

\Rightarrow u = g t_{m a x} = 20 m s^{- 1}

(∵ g = 10 m s^{- 2})

Q. A ball is thrown upwards, it takes $4 sec$ to reach back to the ground. Find its initial velocity:

$30 m s^{- 1}$

$10 m s^{- 1}$

$40 m s^{- 1}$

$20 m s^{- 1}$

Since the ball is thrown upwards and it reaches back,
so time to reach maximum height is half of total time i.e.,
$t_{maximum} = 2 sec$
Also speed at maximum height is zero, so
$o = u - g t_{m a x}$
$\Rightarrow u = g t_{m a x} = 20 m s^{- 1}$
$(∵ g = 10 m s^{- 2})$

Q. A ball is thrown upwards, it takes 4sec to reach back to the ground. Find its initial velocity:

30ms−1

10ms−1

40ms−1

20ms−1