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A train is at rest and it accelerates to a velocity of 100 meters per second. How long does it take to reach that speed?

I can do the work, I just don't know what equation to use.

I know the constant force being created by the train's engine (10,000 Newtons)

I know the mass of the train (5,000 Kg)

I can find out the drag force working against the train at 100 meters per second by using the Drag equation at Wikipedia D=.5pV^2ACd = 150 Newtons

http://en.wikipedia.org/wiki/Drag_equation

Force ----> (object@ 100 M/S velocity) <----Drag+Mass

The thing that kind of confuses me is that drag isn't constant from 0 to 100 M/S. It's steadily increasing. I know this isn't a hard one but it is for me.

Thanks,

Al

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# Homework Help: Which equation do I use to find time to a certain speed?

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