ah, I was tired, I was thinking of 50mph, which is about 25m/sI think your calculation is not quite right Paul, I reckon the deceleration corresponding to 50 kW is higher - would you like to check it?
Force = mass * acceleration => a = f / m
Force * speed = power => f = p / s
so a = (p / s) / m => a = p / (s * m)
a = 50000 / (25 * 1500) = 1.3m/s^2
does that make sense? I'll correct my comment above if so.