A) \[74\,\,m{{s}^{-}}^{2}\]
B) \[55\,\,m{{s}^{-}}^{1}\]
C) \[40\,\,m{{s}^{-}}^{1}\]
D) \[60\,\,m{{s}^{-}}^{1}\]
Correct Answer: A
Solution :
For first ball, \[\operatorname{u} = 0\] \[\therefore \,\,\,\,\,{{s}_{1}}=\frac{1}{2}\,gt_{1}^{2}=\frac{1}{2}\times g{{(18)}^{2}}\] For second ball, initial velocity = v \[\therefore \,\,\,\,\,{{s}_{2}}=\,\,\nu t_{2}^{{}}=\,\,\frac{1}{2}\,g{{t}^{2}}_{2}\] \[{{t}_{2}}\,=\,\,18-6\,\,=\,\,12\,s\] \[\Rightarrow \,{{s}_{2}}={{s}_{2}}=\nu \times 12+\frac{1}{2}\,g{{(12)}^{2}}\] Here, \[{{s}_{1}}={{s}_{2}}\] \[\frac{1}{2}g\left( 1{{8}^{2}} \right)=12\nu +\frac{1}{2}\,g{{\left( 12 \right)}^{2}}\,\,\,\Rightarrow \,\,\,\nu =74\,\,m{{s}^{-1}}\]
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