Two masses of 1kg and 5kg are attached to the ends of a massless string passing over a pulley of negligible weight. The pulley itself is attached to a light spring balance as shown in figure. The masses start moving during this interval, the reading of spring balance will be:

Options

A. more than 6kg
B. less than 6kg
C. equal 6kg
D. none of the above

Answer

B

Explanation

Suppose `T` be the tension in each part of the string passing over the pulley. `T` is given by:
`T=(2m_(1)m_(2)g)/(m_(1)+m_(2))=(2xx1xx5)/(1+5)g=(5)/(3)g`
For equilibrium of the pulley there is an upward force of `2T` acting on the string joining the pulley to the spring. Therefore, reading of spring balance will be `2T=g//3` . So reading will be `10//3kg` which is less than `6kg` .