Application of Newton's Laws of motion

1. Feb 26, 2007

Aggie

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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2. Feb 27, 2007

Edgardo

How did you come to the 271.5?

3. Feb 27, 2007

H_man

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. Feb 27, 2007

Aggie

I came up withthe equation

mg+ Fr = mg cos theta

5. Feb 27, 2007

H_man

That equation does not look right. Where is P?

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

6. Jan 30, 2012