1. The spring is storing
1/2 (240 N/m) (0.40 m)² = 19.2 J ≈ 19 J
of potential energy.
2. When the spring is compressed by 0.30 m, it is storing
1/2 (240 N/m) (0.30 m)² = 10.8 J
so there was a loss of 19.2 J - 10.8 J = 8.4 J.
3. The spring is storing
1/2 (150 N/m) (0.80 m)² = 48 J
of potential energy.
4. Stretching the spring by 0.20 m more has it storing
1/2 (150 N/m) (1.0 m)² = 75 J
so that the extra weight adds 75 J - 48 J = 27 J of energy.
