Question

(2) Why do spring balance shows wrong reading after they had been uses for a long time?​

Answer 1

When a spring balance has been used for a long time, the spring in the balance fatigued and there is loss of strength of the spring. In such a case, the extension in the spring is more for a given load and hence the balance gives wrong readings.

Answer 2

This is because of continuous usage, the wire loses its elasticity and dose not regain it original dimension