A locomotive hauls a train along a level track at a constant speed of 54kmh−1 while delivering a power output of 1.2MW.
a. (i) Calculate the total resistive force acting on the train.
b. (ii) The driver now shuts off the engine and applies brakes that exert a force equal in magnitude but opposite in direction to the resistive force found in part (i). Show that the power associated with the braking force at the instant the speed is 54kmh−1 is −1.2MW. Explain the physical meaning of the negative sign.
c. (iii) Later, the train resumes steady motion at 36kmh−1 under the same resistive force. Determine the power the locomotive must now develop to maintain this lower speed.