A metro train consisting only of a motor coach of mass and three passenger coaches

PHYSICS · Subjective · AP · Physics 1: Algebra-based · Force and Translational Dynamics · Force and Translational Dynamics

Problem

A metro train consisting only of a motor coach of mass

8\,500\,\text{kg}

and three passenger coaches, each of mass

3\,000\,\text{kg}

, moves on a straight horizontal track. Air resistance and track friction together exert a force of

7.5\times10^{3}\,\text{N}

opposite to the motion. The train is required to accelerate uniformly at

1.2\,\text{m\,s}^{-2}

. (a) Calculate the net force that must act on the train to produce the required acceleration. (b) Hence determine the horizontal force that the motor coach must exert to achieve the specified motion. (c) If, after some time, the frictional force rises to

1.0\times10^{4}\,\text{N}

while the motor coach continues to exert the same horizontal force as in part (b), find the new acceleration of the train.

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