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.

Options

A. 70 J
B. 210 J
C. 140 J
D. 350 J

Answer

A

Explanation

`a=((3-20g)/((3+2))=(g)/(5)=2(m)/(s^2)`
Displacement of blocks in the `4^(th)` second
`s=(1)/(2)a(2t-1)=(1)/(2)xx2(2xx4-1)=7m`
Work done by the gravity in the `4^(th)` second is
`(3g-2g)xx7=70J`