Department of Mechanical Engineering, MITS-FET Name: Engineering Mechanics (ME-105) Tutorial.Batch: Autumn Semester 2011-2012 Roll No.: Engineering Mechanics (ME 105) TUTORIAL SHEET-4 1 2 3 Define the term friction. Explain the following terms. a) Coefficient of friction c) angle of repose Block A of mass 12 kg and block B of mass 6 kg are connected by a string passing over a smooth pulley. If coefficient of friction is 0.12 at all surfaces of contact find smallest value of force P to maintain equilibrium. b) angle of friction d) cone of friction 4 Can the system in figure be in static equilibrium in the position shown? The uniform bar AB weight 500 N and the weight of block c is 300 N. Friction at A is negligible, and coefficient of static friction is 0.4 at the other two contact surfaces. Determine the minimum horizontal force P required to hold the crate from sliding down the plane. The crate has a mass of 50 kg and the coefficient of static friction between the crate and the plane is ms = 0.25. 5 The top of the 15 kg ladder has a small roller and at the ground the coefficient of static friction is 0. has a mass of 500 kg and is held in the horizontal position using a wedge al B. The center of gravity of the 250-N crate is located at its geometric center. determine when the crates begin to slide.25. The uniform stone in Fig. 9 .3.35. If the coefficient of static friction is = 0. Does the crate move if P =60 N? The coefficient of static friction between the crate and the floor is 0. 8 The man in Fig.6 7 Crates A and B weigh 200 N and 150 N. Determine the distance s to which the 90 kg painter can climb without causing the 4 m ladder to slip at its lower end A. The mass center of the painter is directly above his feet. They are connected together with a cable and placed on the inclined plane. Assume that the stone does not slip at A. If the angle is gradually increased.3 at the surfaces of contact. respectively.25 and mB = 0. The coefficients of static friction between the crates and the plane are mA = 0. is trying to move a packing crate across the floor by applying a horizontal force P. Determine the minimum force P needed to remove the wedge. The coefficient of static friction between the rope and the tree trunk is 0. The coefficient of static friction at all contacting surfaces is 0.3. If the cow exerts a force of 1100 N on the rope. (a) For α=0.15 and between the farmer’s shoes and the ground. determine if the farmer can successfully restrain the cow. determine the maximum and minimum values which P may have in order not to raise or lower the load. A 80 kg farmer tries to restrain the cow from escaping by wrapping the rope two turns around the tree trunk as shown.3. Value of µ between the cable and the fixed drum is 0.10 Determine the smallest horizontal force P required to lift the 200-kg crate. (b) For P=500 N determine the minimum value which the angle α may have before the load begins to slip. Neglect the mass of the wedge. 12 . 11 A flexible cable which supports the 100 kg load is passed over a fixed circular drum and subjected to a force P to maintain equilibrium.