Homework Help: Just a repost, in case the old isnt seen

Posted by Alexis on Sunday, October 14, 2007 at 6:25pm.

sorry! I never noticed..the mass should be 52000kg sorry about that!

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physics repost - Alexis, Sunday, October 14, 2007 at 6:07pm
so it should be a 52000kg train slows from 25 m/s to 14m/s in 5.0 s. Calculate the work done on the train.

so I found the displacement by using

displacement= 1/2 (v1+v2) (delta t)
and got 97.5

and then I found the force which is F=mg
and got 510120N, then took that force and did W=Fd

and got 49736700J

my textbook says 1.1x10^7J? How is that right? I think I am right?

physics repost - Alexis, Sunday, October 14, 2007 at 6:17pm
I tried to get the answer using the kinetic energy formula, and it works (for the answer of 1.1x10^7), but the only problem is, the homework is for the pages before the kinetic energy, so I would like to know how to figure out the answer without the kinetic energy formula. Thank you for helping me!

Just a repost, in case the old isnt seen - Alexis, Sunday, October 14, 2007 at 6:31pm
HAHA I just got the answer!!!! You don't use F=mg it should be ma!!! Thanks anyways!!

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