Prob. 8–85

Example 5.1: The rope exerts a horizontal force on the stationary 180-lb crate. The coefficient of static friction between the crate and the ramp is us = 0.4. If the rope exerts a 90-lb force on the crate, what friction force is exerted on the crate by the ramp? 20

A crane is used to lower weights into a lake for an underwater construction project. Determine the tension in the rope of the crane due to 3-ft-diameter spherical steel block (density = 494 bm/ft3) when it is (a) suspended in the air and (b) completely immersed in the water.

A 2.4 m ladder rests on a vertical wall as shown in the figure. The ladder has seven rungs and the rungs are spaced 0.30 m apart, and the top and bottom rungs are 0.30 m from their respective ends of the ladder. Surfaces at A and B both have the same coefficient of friction. If a worker weighs 630 N and stands on the middle rung, determine the minimum value of the coefficient of friction so that the ladder does not slide. Neglect the weight of the ladder.