Find how much mass `m` will rise if `4m` falls away. Blocks are at rest and in equilibrium.

Answer

`(8mg)/(k)`

Explanation

Applying WET on block of mass m
`W_g+W_(sp)=K_f-K_i`
Let finally displacement of block from equilibrium is x.
`-mg((5mg)/(k)+x)+1/2k((25m^2g^2)/(k^2))-1/2kx^2=0`
`1/2kx^2+mgx-(15m^2g^2)/(2k)=0`
`x=(3mg)/(k)`
Displacement from initial is `(5mg)/(k)+(3mg)/(k)=(8mg)/(k)`