When a 2.90-kg object is hung vertically on a certain light spring described by Hooke's law, the spring stretches 2.76 cm.
(a) What is the force constant of the spring?
(b) If the 2.90-kg object is removed, how far will the spring stretch if a 1.45-kg block is hung on it?
(c) How much work must an external agent do to stretch the same spring 6.80 cm from its unstretched position