Friction and Pulley Problem

  • Thread starter psycovic23
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  • #1
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"Two blocks are attached to a string that passes over a frictionless pulley. One of the blocks is 4kg and rests on a rough horizontal surface. The other block is a 2kg block that hangs over the edge of the surface. When the system is released, the 2 kg mass falls from rest and attains the speed of 2m/s after traveling a distance of 3 meters"

The first question is "what is the loss in mechanical energy" and I get 56J, which is right according to my teacher. However, the second question is "what is the coefficient of kinetic friction between the 4 kg block and the rough surface?"

What I do is:

Loss in mechanical energy = energy of friction

Thus:

56 = Fd =
56 = umgd =
56 = u * 4 * 9.8 * 3m

and I get .47. However, the answer is .40. What am I doing wrong?
 

Answers and Replies

  • #2
Astronuc
Staff Emeritus
Science Advisor
18,924
2,235
How did you obtain 56 J?

Also think, what is the tensile force in the string?

There is friction, and there is the force required to accelerate the 4 kg mass laterally. What is the lateral acceleration of the 4 kg block?
 

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