Homework Help: Physics

Posted by Lena on Friday, April 17, 2009 at 4:55am.

Two steel blocks are at rest on a frictionless horizontal surface. Block X has a mas of 3.0 kg ans is attacthed by means of a light taut string to block Y that has a mass of 12 kg. A force of 45 N (E) is applied to block x. Calculate the force block Y exerts on block x.

I don't have any idea of how to go about do this question. I think it's related to newton's 3rd law about action-reaction forces but I don't know any else. Could someone please guide me in the right direction? Thanks

Physics - drwls, Friday, April 17, 2009 at 7:39am
The 45N force accelerates both masses at a rate
a = 45/(3 + 12) = 3 m/s^2
The taut string between X and Y applies an accelerating force to block Y that equals f = m a = 12 kg * 3 m/s^2 = 36 N. The reaction force upon block X is 36 N in the opposite direction (West).

You are correct that Newton's third law is involved

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