A sping of spring constant k is attached to the ceiling. A block of mass M is attached to its lower end and is released suddenly.
(ii) Find its speed at the instant it passes throught the equilibrium position.

Explanation

When the block is equilibrium (i.e. `F_("net")=0`)
`kx_(@)=Mg`
`impliesx_(0)=(Mg)/(k)`
`therefore` Applying work energy therom for motion from (a) to (b)
`Mgx_(0)-(1)/(2)kx_(0)^(2)=(1)/(2)M(V_(0)^(2)-0)`
`impliesMg((Mg)/(k))-(1)/(2)k((Mg)/(k))^(2)=(1)/(2)MV_(0)^(2)`
`impliesv_(0)=gsqrt((M)/(k))`