Answer
$1.4\space m/s^{2}$
Work Step by Step
Here we use the equation $V=u+at$ to find the acceleration.
Let's apply this equation to the second phase of acceleration.
$V=u+at$ ; Let's plug known values into this equation.
$3.4\space m/s^{2}=u+1.1\space m/s^{2}\times 1.2\space s$
$u=2.1\space m/s$
Thus, the starting velocity of the second phase = 2.1 m/s ; This is equal to the final velocity of the first phase of the acceleration.
Let's apply above equation to the first phase of acceleration.
$V=u+at$ ; Let's plug known values into this equation.
$2.1\space m/s^{2}=0+a_{1}\times 1.5\space s$
$a_{1}=1.4\space m/s^{2}$
