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So we got a generic pulley problem like this:
http://www.screencast.com/users/trinhn812/folders/Jing/media/9fe7c5ed-2d5d-4a1e-be22-ca3bbd2b78cc
There is kinetic friction on box A. Pulley is massless.
Which of the following is true:
I. The magnitude of the normal force equals the weight of M1 by Newton's 3rd law
II.The normal force is proportional to the tension in the rope by Newton's 3rd law
III. The normal force is related to friction, by Newton's 2nd law
IV, The normal force is in the direction opposite of weight by Newton's 2nd law
Answer choices only included 2 of the above and I got this right based on that. But I think question really boggled me.
I. True. I agree. basic definition
II. False. BR says the whole thing is untrue, but I think that if the statement said it was according to Newton's 2nd law, it would be true. F(kinetic)=uN=T if acceleration is zero. So shouldn't normal force should be proportional to tension according the 2nd law?
III. False. Hmm Friction = uN so why isn't it related.
IV. True. This seems a bit of a stretched and BR's explanation isn't that strong. But if they stretched it this much, III should be true..
http://www.screencast.com/users/trinhn812/folders/Jing/media/9fe7c5ed-2d5d-4a1e-be22-ca3bbd2b78cc
There is kinetic friction on box A. Pulley is massless.
Which of the following is true:
I. The magnitude of the normal force equals the weight of M1 by Newton's 3rd law
II.The normal force is proportional to the tension in the rope by Newton's 3rd law
III. The normal force is related to friction, by Newton's 2nd law
IV, The normal force is in the direction opposite of weight by Newton's 2nd law
Answer choices only included 2 of the above and I got this right based on that. But I think question really boggled me.
I. True. I agree. basic definition
II. False. BR says the whole thing is untrue, but I think that if the statement said it was according to Newton's 2nd law, it would be true. F(kinetic)=uN=T if acceleration is zero. So shouldn't normal force should be proportional to tension according the 2nd law?
III. False. Hmm Friction = uN so why isn't it related.
IV. True. This seems a bit of a stretched and BR's explanation isn't that strong. But if they stretched it this much, III should be true..