If only gravity and springs do work, mechanical energy is conserved. Non-conservative work (friction, drag) must be moved to the work–energy side: T1+V1+U_{1 o2}^{nc}=T2+V2.
T
Kinetic energy ½mv² or ½Iω²
V
Potential: mgh + ½kx²
Step-by-step solved example
A 2 kg mass drops 3 m onto a spring k=200 N/m from rest, contacting at unstretched. Max compression?
Height to speed: T+V conserved along the path (no friction).
1. Energy
mg(3+δ)=½ k δ² (datum at max compression).
2. Solve
19.62(3+δ)=100 δ² → δ≈0.85 m (positive root).
Answer: δ ≈ 0.85 m
10 practice questions
0/10 correct
1.Friction violates mechanical-energy conservation because
2.V_spring is
3.A particle at rest at height h has T+V =
4.Speed after falling h (no spring) is
5.Rotating body uses T=
6.Datum for V_g may be placed
7.If a cable tension is internal to the system of both masses