An object of mass 5.00 kg is attached to a spring with a force constant of 300 N/m. It is oscillating on a horizontal frictionless surface with an amplitude of 2.00 m. A 8.00 kg object is dropped vertically on top of the 5.00 kg object as it passes through its equilibrium point. The two objects stick together. By how much does the amplitude of the vibrating system change?

Answer 1

Why would the amplitude change? The deflection is in the horizontal. Adding mass should not change that deflection (but will change the period (frequency)).