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# A particle starts from rest at $t=0$ and undergoes an acceleration 'a' in $m/s^2$ with 't' in sec as shown

Which of the following represents velocity v in m/s and time t in seconds

For interval 0 to 2 sec
$u=0\;a=3\;t=2$
$v=u+at=6 m/s$
for $2\; to \;4s$
$a=-3,\;u=6,\;t=2$
$v'=+6+(-3) \times 2=0$
Hence a is the correct answer.

edited Jan 25, 2014 by meena.p