Question

A frictionless pulley of negligible weight is suspended from a spring balance. Masses of 1kg and 5kg are tied to the two ends of a string which passes over the pulley. The masses move due to gravity. During motion, the reading of the spring balance will be :

(A) 5/3kgwt

(B) 10/3kgwt

(C) 6kgwt

(D) 3kgwt

Answer 1

(B) 10/3kgwt

Forces acting at 1 kg load, 5 kg load and pulley are shown in figure. Let us assume 1 kg load moves upward with acceleration a and 5 kg load moves downward with acceleration a. Let T be the tension in the string.   at 1 kg load :-   

T - g = a ..................(1) 

at 5 kg load :-   T - 5g = -5a ...............(2)   

By solving the above two equations, we get a = (2/3)g  and T = (5/3)g   

Hence tension in the spring, 2T = (10/3)kgwt