Respuesta :

5.635m/s2 is the acceleration of the train
Acceleration = (v - u)/t        u = 50m/s, v = 5m/s, t = 8s

                       = (5 - 50) /8  = -45/8 = -5.625 m/s²


Acceleration = -5.625 m/s², so it actually decelerated by 5.625 m/s² because of the negative sign.