A) \[30\,m{{s}^{-1}}\]
B) \[10\,m{{s}^{-1}}\]
C) \[40\,m{{s}^{-1}}\]
D) \[20\,m{{s}^{-1}}\]
Correct Answer: D
Solution :
Since, the ball is thrown upwards and it reaches back, so time to reach maximum height is half of total rime i.e.,\[{{t}_{\max }}=2s.\] Also speed at maximum height is zero, so \[0=u-g{{t}_{\max }}\] \[\Rightarrow \] \[u=g{{t}_{\max }}=20\,\,m{{s}^{-1}}\]\[(\because g=10\,\,m{{s}^{-2}})\]
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