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Question
A stone thrown vertically upwards takes 3 s to attain maximum height. Calculate
- initial velocity of the stone
- maximum height attained by the stone. (Take g = 9.8 ms−2)
Solution
Initial velocity of the stone = u =?
At highest point, final velocity = v = 0
Time = t = 3s
Acceleration = a = −g = −9.8 ms−2
Maximum height attained by stone = S = h = ?
(i) v = u + at
0 = u + (−9.8) 3
u = 9.8 × 3 = 29.4 ms−1
(ii) Now, S = ut + `1/2` at2
h = `(29.4)3+1/2(-9.8)(3)^2` = 88.2 − 4.9 × 9
= 88.2 − 44.1 = 44.1 m
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