Understanding Power Calculation: 1.5MW vs 1.47MW Explained

[Bix]

Homework Statement

'Find the max power of a train engine travelling level at 50 metres per second if total resistance to motion is 30 KiloNewtons.

Relevant Equations

'Find the max power of a train engine travelling level at 50 metres per second if total resistance to motion is 30 KiloNewtons.

In answer to this I get power = force times velocity so 30000 x 50 = 1500000 = 1.5 Mega Watts. My answer book says 1.47 Mega Watts. I can see how 1.5MW minus 30KW = 1500000 - 30000 = 1.47MW. Also I can see that power times gravity of 9.8 = 1.5 MW times 9.8 N gives the same answer. I can't see how you should subtract the force from the sum of the force and the distance, or how vertical gravity can reduce the speed of a horizontally moving train. Thanks :)

 

[haruspex]

You did not need to post this here again. Your original has already been moved to this forum at https://www.physicsforums.com/threa...train-given-the-resistance-to-travel.1000842/.
(Where there are already some replies, and you have a much better title for the thread!)

 

[Mark44]

Locked as a duplicate of another post.