First slide

Vertical projection from ground

Question

A bullet fired vertically up from the ground reaches a height 40 m in its path from the ground and it takes further time 2 seconds to reach the same point during descent. The total time of flight is (g = 10 m $s^{- 2}$ )

Moderate

A

4s
B

3s
C

6s
D

8s

Solution

$T i m e i n t e r v a l = \frac{2 v}{g} \Rightarrow 2 = \frac{2 \times v}{10} \Rightarrow v = 10$
$v^{2}$ = $u^{2}$ +2as ⇒ 102 = u2 - 2 x 10 x 40
$u^{2}$ = 100 +800 ⇒ $u^{2}$ = 900 ⇒ u = 30
$T = \frac{2 u}{g} = \frac{2 \times 30}{10} = 6$

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