A) zero
B) 24 m/s
C) 25 m/s
D) none of these
Correct Answer: B
Solution :
Let the body goes from \[A\] to \[B\] in \[{{t}_{1}}\] sec and comes back from \[B\] to \[A\] in \[{{T}_{2}}\] sec. and let the distance between \[A\] and \[B\] be\[s\]. \[\therefore\] \[{{t}_{1}}=\frac{s}{20}\] and \[{{t}_{2}}=\frac{s}{30}\] Total distance travelled \[=s+s=2s\] Total time taken \[={{t}_{1}}+{{t}_{2}}\] \[=\frac{s}{20}+\frac{s}{30}=\frac{5s}{60}\] \[\therefore\] Average velocity \[=\frac{2s}{{{t}_{1}}+{{t}_{2}}}\] \[=\frac{2s}{5s}\times 60=24\,\,m/s\]
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