The two blocks in an Atwood machine have masses 2.0 kg and 3.0 kg. Find the work done by gravity during the fourth second after the system is released from rest.

Explanation

Pulling force `=3g-2g=g`
Total mass to be pulled `=3+2=5`
acceleration `a=(g)/(5)=(10)/(5)=2(m)//(s^2)`
Displacement of block in the first 2 s of motion
`s=ut+(1)/(2)at^2=0+(1)/(2)xx2xx2^2=4m`
Work done by the gravitational force
`W=30xx4+(-20xx4)=40J`