question_answer

A ball is thrown up and attains a maximum height of 19.6 m. Its initial speed was (a) \[9.8m{{s}^{-1}}\]                     (b) \[44.3m{{s}^{-1}}\] (c) \[19.6\text{ }m{{s}^{-1}}\]                     (d) \[98\text{ }m{{s}^{-1}}\]

Answer:

\[{{h}_{max}}=19.6\text{ }m\] \[u=?\] \[v=0\]                                 \[(\because h={{h}_{max}})\] \[g=9.8\text{ }m/{{s}^{2}}\] We know \[{{v}^{2}}{{u}^{2}}=2gh\] \[\Rightarrow \]\[{{0}^{2}}{{u}^{2}}=2\times (9.8)\times 19.6\] \[\Rightarrow \]\[{{u}^{2}}=19.6\times 19.6\] \[\Rightarrow \] \[u=19.6\text{ }m/s\]