A) (Take\[g=10\text{ }m{{s}^{-2}}\]) 4m
B) 2m
C) 1 m
D) 0.4 m
Correct Answer: D
Solution :
Key Idea At a given height the half of the kinetic energy of the body is equal to its potential energy. Initial kinetic energy of the body \[=\frac{1}{2}m{{v}^{2}}\] \[=\frac{1}{2}m\,{{(4)}^{2}}=8m\] Let at height h, the kinetic energy reduces to half, i.e., it becomes 4 m. It is also equal to potential energy. Hence, \[mgh=4\,m\] or \[h=\frac{4}{g}\,=\frac{4}{10}\,=0.4\,m\]
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