A) 15 J
B) 11.25 J
C) 8.44 J
D) none of these
Correct Answer: C
Solution :
After first hit \[K.{{E}_{1}}\,\,=\,\,{{e}^{2}}\,K.E\] \[3/4\,\,K.E=\,\,{{e}^{2}}\,K.E\text{ }\Rightarrow \,\,{{e}^{2}}=3/4\] K.E. after third hit \[={{e}^{2(3)}}.\,\,K.E\,\,=\,\,27/64\,(mgh)\] \[=\,\,\frac{27}{64}\,\left( \frac{1}{2}.10.4 \right)\] \[=\,\,27\left( \frac{5}{16} \right)\,\,=\,\,\frac{135}{16}\,\,=\,\,8.44\,\,J\,\,\]
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