Answer to Question #255135 in Classical Mechanics for Sara

Question

Block B in Figure weighs 711 N. The coefficient of static friction between block and table

is 0.25; angle θ is 300

; assume that the cord between B and the knot is horizontal. Find the

maximum weight of block A for which the system will be stationary?

Answer 1

Equilibrium of forces in horizontal and vertical direction gives us the following (T - tension in the string at the angle theta):

$$B:\mu W_B=T\cos\theta,\\ A:W_A=T\sin\theta.\\\space\\ T=\mu W_B/\cos\theta=205\text{ N},\\ W_A=205·\sin30°=103\text{ N}.$$