PHYSICS · Multi-part · CBSE · Physics · Laws of Motion · Laws of Motion
Problem
A 4.0kg block rests on a 25∘ rough incline. A rope attached to the block pulls parallel to the incline; the tension T is slowly increased from 0N to 50N. The coefficients of friction between the block and the incline are μs=0.60 and μk=0.45. Air resistance is negligible.
(a) Derive an expression for the normal force exerted on the block in terms of known quantities, and calculate its numerical value.
(b) Determine the exact value of the tension at which the block first begins to move up the incline.
(c) Sketch a quantitative graph of the magnitude of the friction force acting on the block as a function of tension from 0N to 50N. Label all critical points, including any change in the sign of the friction force.
(d) For a tension of 40N, calculate the block’s acceleration, indicating its direction along the incline.
(e) Explain, using Newton’s laws, why the direction of the static friction force may reverse as the tension increases, and how this reversal is represented on your graph from part (c).