Posted by KC on Monday, April 6, 2009 at 11:51pm.
I don't know where to start with this one. "Find the work done accelerating a 2 kg box from 2m/s to 3 m/s." Can't find acceleration because I don't know time. In fact, I don't see how any of the kinematic equations can help me out to find either distance or acceleration so that I can then find Force and then work. What am I missing?

Physics  drwls, Tuesday, April 7, 2009 at 2:32am
You don't need to know the time or the acceleration. Just compute the increase in kinetic energy.
delta KE = work
= (1/2)*(2 kg)[3^2  2^2]

Physics  KC, Tuesday, April 7, 2009 at 7:35am
Thanks. Is this the only way to calculate because in our lesson we only learned the formula for work =fd? We've haven't done KE yet.

Physics  drwls, Tuesday, April 7, 2009 at 9:36am
You could assume a uniform acceleration time, T. You would find that the force required would be inversely proportional to T, and the distance would be proportional, so that it would cancel out when calculating F*d.
Vav*T = (V2 + V1)/2 * T = d
F = M a = M * (V2  V1)/T
F*d = (1/2) M (V2^2  V1^2)

Physics  KC, Tuesday, April 7, 2009 at 12:09pm
Thank you very much!
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