Find the amplitude and frequency of the vibrations

[JustinLiang]

Homework Statement

A 1.50-kg ball and a 2.00-kg ball are glued together with the lighter below the heavier one. The upper ball is attached to a vertical ideal spring of force constant 165 N/m, and the system is vibrating vertically with an amplitude of 15.0 cm. the glue connecting them breaks at the lowest point. Find the amplitude and frequency of the vibrations after the lower ball has come loose.

Homework Equations

w=sqr(k/m)
F=-kx

The Attempt at a Solution

The answer is 23.9cm but I don't see how the amplitude could be larger if mass is removed... Unless of course I misread the question...

I initially tried F=kx --> mg=kx --> x=0.12m

 

[JHamm]

Just because there is no net force doesn't mean the object stops, if the system was horizontal then in the middle of the oscillation there would be no net force but the weights would certainly move. You want the work done by the spring pulling up to be canceled by the work done by gravity pulling down and by the spring pushing down.