Answer :
- Initial velocity=u=0m/s(As it starts from rest)
- Final velocity=v=120m/s
- Distance between course=s=400m
- Acceleration be a
Apply third equation of kinematics
[tex]\\ \rm\hookrightarrow v^2-u^2=2as[/tex]
Isolate the equation for a
[tex]\\ \rm\hookrightarrow a=\dfrac{v^2-u^2}{2s}[/tex]
[tex]\\ \rm\hookrightarrow a=\dfrac{v^2}{2s}[/tex]
[tex]\\ \rm\hookrightarrow a=120^2/800[/tex]
[tex]\\ \rm\hookrightarrow a=18m/s^2[/tex]