A) \[10\]
B) \[15\]
C) \[20\]
D) \[30\]
Correct Answer: A
Solution :
Let the initial velocity = u and acceleration = a In first case \[{{s}_{1}}=utl1+\frac{1}{2}at_{1}^{2}\] \[200=2u+2a\] \[(\because \,\,\,{{t}_{1}}=2s)\] \[u+a=100\] ?.(i) In second case \[{{s}_{2}}=u{{t}_{2}}+\frac{1}{2}at_{2}^{2}\] \[420=6u+18a\] \[(\because \,\,\,{{t}_{2}}=2+4=6\,s)\] \[3a+u=70\] Solving Eqs. (i) and (ii), we get \[a=-15m/{{s}^{2}}\] and \[u=115m/s\] \[v=u+at\] \[=115-15\times 7=10m/s\]
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