A Very Light Ideal Spring of Spring Constant (Force Constant)

Short Answer

A very light ideal spring of spring constant (force constant) 2.5 N/cm is 15 cm long when
nothing is attached to it. It is now used to pull horizontally on a 12.5-kg box on a perfectly
smooth horizontal floor. You observe that the box starts from rest and moves 96 cm during
the first 1.6 s of its motion with constant acceleration. How long is the spring during this
motion?