Physics??

[ajc]

Ok guys, who on my friends list is good at physics. I'm a complete moron and have never been able to figure out static friction problems. It's not explained well in the book. And I suppose they're easy enough, but for some reason I always mess them up. I just took a test and can't figure out if I answered the question right

Comments

[mfisher]

It's been a long time since I've done basic physics, but I think this is the jist of it.

Fg = ma = 24kg * 9.8 m/s = 235.2N
Ff = muk * FN = .04 * 235.2N = 94.08N

Since there's already -35N working against you, Fneeded = Ff + 35N = 129.08N.

If you were accelerating the object itself without any resistance or other forces, Fbasic = ma = 24kg * 3.5m/s = 84N.

Therefore, you need Ftotal = Fneeded + Fbasic = 129.08N + 84N = 213.08N.

[ajc]

Hmm, I think that's actually the answer to static friction. How much force is needed to start moving the object and then accelerate to 3.5 m/s. In this case, the object was already in motion.