To calculate the acceleration of the truck, we use the equation of motion
[tex]v = u + at[/tex]
Here, v is final velocity of the truck, u is initial velocity of truck, a is acceleration of the truck and t is time taken.
Given, u = 6 m/s, v = 14 m/s and t = 4 s.
Substituting these values in above equation, we get
[tex]14 \ m/s = 6 \ m/s + a \times 4 \ s \\\\ a = \frac{14 \ m/s - 6 \ m/s}{ 4 \ s } = 2 \ m /s^2[/tex].
Thus, the truck acceleration is [tex]2 \ m /s^2[/tex]