what force (in n) must each engine exert backward on the track to accelerate the train at a rate of 3.00 ✕ 10−2 m/s2 if the force of friction is 5.00 ✕ 105 n, assuming the engines exert identical forces? this is not a large frictional force for such a massive system. rolling friction for trains is small, and consequently trains are very energy-efficient transportation systems.