A) 11.5 seconds
B) 21 seconds
C) 10 seconds
D) 14 seconds
Correct Answer: A
Solution :
The time taken by the stone to reach the lake \[{{t}_{1}}=\sqrt{\left( \frac{2h}{g} \right)}=\sqrt{\left( \frac{2\times 500}{10} \right)}=10\,sec\] (Using \[h=ut+\frac{1}{2}g{{t}^{2}}\]) Now time taken by sound from lake to the man \[{{t}_{2}}=\frac{h}{v}=\frac{500}{340}\approx 1.5\sec \] Þ Total time \[={{t}_{1}}+{{t}_{2}}=10+1.5=11.5\sec .\]
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