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Question
A boy drops a stone from a cliff, reaches the ground in 8 seconds. Calculate
- final velocity of stone
- height of cliff. (Take g = 9.8 ms−2)
Solution
Initial velocity = u = 0
Time = t = 8s
Final velocity = v = ?
Height of cliff = h = ?
Acceleration = a = + g = + 9.8 ms−2
(i) v = u + at
v = 0 + 9.8 (8)
v = 78.4 ms−1
(ii) S = ut + `1/2` at2
h = `0(8)+1/2(9.8)(8)2`
h = 0 + 4.9 × 64
h = 313.6 m
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