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?

Question

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?

drwls · Answer

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]

KC · Answer

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.

drwls · Answer

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)

KC · Answer

Thank you very much!