I got 225000N for this question but my teacher's marking (which I'm not convinced with says 25000N - he's probably right though but I must check as I can not ask him as its the christmas holidays and our exam is pretty much the first day back)
See what you make of it! Please =P
A train of mass 200000kg is moving at a constant velocity of 25m/s, it then brakes and has constant decelleration and comes to rest in 40s. In this stage there is no driving force produced by the train's engine, but a retarding force produced by the train's brakes. There is also a constant resistance force on the train of magnitude 100000N throughout the brakin. Find the retarding force produced by the breaks.