Question

Two masses 8 kg and 12 kg are connected at the two ends of a light inextensible string that goes over a frictionless pulley. Find the acceleration of the masses, and the tension in the string when the masses are released.

Answer 1

The given system of two masses and a pulley can be represented as shown in the following figure:



Smaller mass, m1 = 8 kg

Larger mass, m2 = 12 kg

Tension in the string = T

Mass m2, owing to its weight, moves downward with acceleration a,and mass m1 moves upward.

Applying Newton’s second law of motion to the system of each mass:

For mass m1:

The equation of motion can be written as:

T – m1g = ma … (i)

For mass m2:

The equation of motion can be written as:

m2g – T = m2a … (ii)

Adding equations (i) and (ii), we get:



… (iii)



Therefore, the acceleration of the masses is 2 m/s2.

Substituting the value of a in equation (ii), we get:



Therefore, the tension in the string is 96 N.