**Example 3:** Determine the magnitude of
P needed to have impending tipping.

Given: W = 250 lb, a = 32 in., b =
72 in., h = 66 in, and m_{s} =
0.4.

**Solution:**

We begin by first calculating the maximum friction force that can occur at the contact surface.

For tipping to be the impending motion, the normal force must be located at the right edge of the block. In that case the moment due to P about the right edge will be equal to that due to weight of the block. Based on this equality, we determine P to be

Since P<F_{s}, the block is on the verge of
tipping over with no possibility of sliding.