A) 120 min
B) 80 min
C) 30 min
D) 20 min
Correct Answer: D
Solution :
\[A={{A}_{0}}{{\left( \frac{1}{2} \right)}^{n}}\]\[\Rightarrow 30=240{{\left( \frac{1}{2} \right)}^{n}}\]\[\Rightarrow {{\left( \frac{1}{2} \right)}^{3}}={{\left( \frac{1}{2} \right)}^{n}}\]Þ n=3 \ \[\frac{t}{{{T}_{1/2}}}=3\] \[\frac{{{v}^{2}}}{r}=\frac{{{n}^{2}}{{r}^{2}}}{4{{\pi }^{2}}{{m}^{2}}{{r}^{2}}}\]= 20 min.
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