PHYSICS · Multi-part · A Level · Physics · Mechanics and materials · Mechanics and materials
Problem
Block A of mass 2.0kg is connected by a light, inextensible string to block B of mass 3.0kg. The string passes over a small frictionless pulley at the edge of a horizontal table, so that block A rests on the table and block B hangs vertically. The coefficient of kinetic friction between block A and the table is μk=0.15. A student pulls horizontally on block A with a constant force of 20N directed away from the pulley so that the system accelerates.
(a) Draw a clearly labeled free-body diagram for each block.
(b) Derive an expression for the magnitude of the acceleration of the system in terms of the given quantities and fundamental constants, showing each algebraic step.
(c) Calculate the numerical value of the acceleration, including the correct SI units.
(d) Determine the tension in the string while the blocks are accelerating, and explain how the value obtained is consistent with the free-body diagrams from part (a).