Example 4: The block has a mass of 100 kg. If the coefficient of static friction between the block and the surface is 0.25, determine

a. the force P needed for the block to have impending slipping
b. the angle of static friction.
c. Is tipping a possibility?


Part a: We begin by drawing the free-body diagram of the block and writing the two force equilibrium equations.

figure equation

Since the condition is impending slipping, the friction force is related to the normal force as


Substituting for F and solving the two equilibrium equations gives


Part b: the angle of static friction is the angle of the resultant force at the surface of contact, and is found as


Part c: To determine if tipping is a possibility, we solve for hmax and compare it to h= 60 in. Using the equilibrium of moments, we find


Since hmax>h, no tipping will occur.