A) 8 m/sec
B) 4 m/sec
C) 6 m/sec
D) 7 m/sec
Correct Answer: B
Solution :
Given: \[u=10\,\,m/s,\,\,t=5\sec ,\,\,v=20\,\,m/s\] Now, \[v=u+at\] \[\therefore \] \[20=10+a\times 5\] \[\Rightarrow \] \[a=2\,\,m/{{s}^{2}}\] Let \[{{u}_{1}}\] be the velocity of the particle before \[t=3\sec ,\,\,{{v}_{1}}=u=10\,\,m/s\]. Then from the relation, \[{{v}_{1}}={{u}_{1}}+at\] \[10={{u}_{1}}+2\times 3\] or \[{{u}_{1}}=\mathbf{4}\,\,\mathbf{m/sec}\].
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