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Weight of 2 Blocks on an Incline

  • Thread starter Sean Smith
  • Start date
  • #1

Homework Statement


Block B rests on Block A. Block B is restrained with a string, while Block A slides down the incline. During the time Block A is between Block B and the inclined plane, Block A slides with constant velocity. If the weight of Blocks A and B are both w, and the coefficient of friction is the same between Block A and B and between Block A and the plane, find the value of the coefficient of friction u. [The angle of the incline is 45].

Homework Equations


The professor's solution has a free body diagram for Block A, with two frictional forces and a normal force. This I understand, but he draws weight straight down with magnitude w+w. I thought this was incorrect, as Block A only experiences a Normal force from Block B.

The Attempt at a Solution


The rest of the problem is inconsequential, but my proposed diagram for Block A has 2 frictional forces up the slope, Normal A normal to the slope, Normal B perpendicular to the surface between Blocks A and B, and weight of w.
 

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Answers and Replies

  • #2
Stephen Tashi
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This I understand, but he draws weight straight down with magnitude w+w. I thought this was incorrect, as Block A only experiences a Normal force from Block B.
If block B wasn't there, wouldn't you still draw a force of w acting on block A ?
 
  • #3
If block B wasn't there, wouldn't you still draw a force of w acting on block A ?
My bad wording, I thought that Block A would have Weight w and Normal force from B. I drew this in the picture I attached to the original post if you'd like to take a look. (:
 
  • #4
Stephen Tashi
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I can't tell anything from that picture.
 
  • #5
haruspex
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The attached picture looks fine, but I presume this is your picture, not your professor's. Without an exact reproduction of what your professor said/drew it will be impossible to tell whether you simply misunderstood. Do you arrive at different answers?
 

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