Application of Newton's Laws of motion

  • #1
A block of mass 20kg is pushed against a vertical surface at an angle of 30 degrees as shown. The coefficient of friction between the surface and the block is 0.2. What is the minimum magitude of P to hold the block still?

I got 271.5 when I tried but the answer is 202.2


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Answers and Replies

  • #2
How did you come to the 271.5?
  • #3
Have you taken into account the fact that the frictional force will depend also on P, ie how strongly it is being pressed against the wall?
  • #4
I came up withthe equation

mg+ Fr = mg cos theta
  • #5
That equation does not look right. Where is P?

Also how do you determine Fr. You need another equation right?

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