(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Your hand presses a block of mass m against a wall with a force F acting at an angle . Find the minimum and maximum possible values of abs(F) that can keep the block stationary, in terms of m, g, theta, and us (the coefficient of static friction between the block and the wall.)

2. Relevant equations

abs(normal force) = F*cos(theta)

Static Friction = Vertical component of net forces unless they are > abs(us*abs(normal force))

3. The attempt at a solution

The following must be true for the block not to move:

abs(F)*sin(theta) - mg >= -(us*abs(F)*cos(theta))

abs(F)*sin(theta) - mg <= us*abs(F)*cos(theta)

The vertical component (always positive) of the force, minus the force of gravity, needs to be less than the coefficient of static friction times the normal force (which is equal to the horizontal component of the applied force).

It also needs to be greater than the negative equivalent of the max static force.

My problem is that the applied force cancels out of the equations, and I can't give an answer that shows the upper and lower limits of the force since they cancel out. Any hints?

Thanks.

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# Homework Help: Maximum and minimum values of a force to keep a block pinned.

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