A) 75 m/s
B) 55 m/s
C) 40 m/s
D) 60 m/s
Correct Answer: A
Solution :
Clearly distance moved by 1st ball in 18s = distance moved by 2nd ball in 12s. Now, distance moved in 18 s by 1st ball \[=\frac{1}{2}\times 10\times {{18}^{2}}=90\times 18=1620\text{ m }\] Distance moved in 12 s by 2nd ball \[=ut+\frac{1}{2}g{{t}^{2}}\text{ }\therefore \text{1620=12v+5}\times \text{144}\] \[\Rightarrow \text{v=135-60=75 m}{{\text{s}}^{-1}}\]
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