A) 4 m
B) 2 m
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, ie, it becomes \[4m.\]It is also equal to potential energy. Hence, \[mgh=4m\] or \[h=\frac{4}{8}=\frac{4}{10}=0.4\,m\]
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