CBSE Class 9 Answered
A boy on a cliff 19.6m high drops a stone. 1 second later he throws a second stone after the first. They both hit the ground at the same time. With what speed did he throw the second stone?
Asked by aahnik.mohanty | 24 Dec, 2017, 20:29: PM
time taken for the first stone to hit the ground is given by
![begin mathsize 12px style S space equals space u cross times t plus 1 half g cross times t squared u space equals space i n i t i a l space v e l o c i t y space equals space 0 semicolon space space space space g space i s space a c c e l e r a t i o n space d u e space t o space g r a v i t y semicolon space space space t space minus space t i m e t space equals space square root of fraction numerator 2 S over denominator g end fraction end root space equals space square root of fraction numerator 2 cross times 19.6 over denominator 9.8 end fraction end root equals space 2 space s end style](https://images.topperlearning.com/topper/tinymce/cache/ea5c762fe9168a03f742153e921ed3f0.png)
hence second stone takes only 1 s to reach the ground
![begin mathsize 12px style S space equals space u cross times t space plus space 1 half cross times g cross times t squared space 19.6 space equals space u plus 1 half cross times 9.8 h e n c e space u space equals space 14.7 space m divided by s end style](https://images.topperlearning.com/topper/tinymce/cache/a18f186ddf2ccd813a5da4e4f1124ec0.png)
Answered by | 24 Dec, 2017, 22:05: PM
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