Question

Calculate the kinetic energy accquired by a system of two masses of 5 kg and 4 kg shown in (i) Fig. (a) (ii) Fig. (b) is 4 s. Take g = 10 ms^-2 and the pulleys as well as the surfaces to be frictionless and ideal. The system is let go from rest in both cases.

Answer 1

Case (i) 

Mass, the FBD is as shown. The equation of motion of the two masses is

For 4 kg mass :mg – T = ma .....(1) 

For 5 kg mass T = Ma .....(2) 

From (1) and (2) we have

Case (ii) 

The 5 kg mass will move downwards and 4 kg upwards. Let T be the tension in the string. Using free body diagram (FBD) we get