Question:
A body projected vertically upward from the top of tower with speed u takes 9 s to reach the ground.Another body projected vertically downward with same speed u from the same point takes 4 s to reach the ground. Height of the tower is?
Answer:
When the body is projected vertically upwards, using the formula, with the formula v = u + at,
where v = 0
a = -9.8 m/s2
t = 9 s
We get, 0 = u - 88.2
Therefore, u = + 88.2 m/s
Now, when the body is projected vertically downwards, again using the formula, S = ut + 1/2 at2
t = 4s
a = 9.8 m/s2
We get, S= 4u + 78.4
So, S = (4 x 88.2) + 78.4
= 431.2 metres is the height of the tower.
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