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Find the resistance to motion

A Level Further Maths
4. A train of mass 100tonnes, working at a power of 150kW, moves at a constant speed of 15 m/s.
i) Find the resistance to motion of the train.

I'm a bit stuck on how to find the resistance to motion. So far I've converted the units

100tonnes : 100 000kg
150kW : 150 000 W

and I've used

Work Done = 1/2*mv^2

to get

1/2 * 100 000 * 15^2 = 11 250 000J

Can anyone tell me what to do from here?

Reply 1

slapsticjoe

this is what you do
you use the fact that power = force x velocity and because it’s going at constant speed the forces are balanced so, the resistance to motion is equal to the forward force which is just power divided by velocity, so it’s just 150000/15 which is 10000N