A) 74 m/s
B) 64 m/s
C) 84 m/s
D) 94 m/s
Correct Answer: A
Solution :
For first ball, initial velocity u = 0 \[{{s}_{1}}=\frac{1}{2}gt_{1}^{2}=\frac{1}{2}\times g\times {{(18)}^{2}}\] For second ball, initial velocitu \[-v\] \[{{s}_{2}}=v{{t}_{2}}+\frac{1}{2}g{{t}^{2}}\] \[{{t}_{2}}=18-6=12s\] \[{{s}_{2}}=v\times 12+\frac{1}{2}g{{(12)}^{2}}\] Here, \[{{s}_{1}}={{s}_{2}}\] \[\frac{1}{2}g{{(18)}^{2}}=12v+\frac{1}{2}g{{(12)}^{2}}\] \[v=74m/s\]
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