A 50-lb block rests on a rough inclined plane. If the coefficient of friction between the block and the plane is 0.50, calculate the inclination of the plane with the horizontal when motion impends. 6.33 If in Problem 6-32 the plane has an inclination with the horizontal of 20°, calculate
a. the frictional resistance when the block is at rest
b. the force parallel to the plane necessary for motion to impend up the plane
c. the force parallel to the plane necessary to prevent motion down the plane