question_answer

Read each of the statements below care- fully and state, with reasons, if it is true or false. (a) When a material is under tensile stress, the restoring forces are caused by interatomic attraction while under compressional stress, the restoring forces are due to inter-atomic repulsion. (b) A piece of rubber under an ordinary stress can display 1000% strain: yet when unloaded returns to its original length. This shows that the elastic restoring forces in a rubber piece are strictly conservative. (c) Elastic restoring forces are strictly conservative only when Hooke's law is obeyed.

Answer:

                (a) True. In tensile stress, the interatomic separation becomes greater than equilibrium separation and the interatomic forces are attractive. In compressional stress, the interatomic separation becomes less than\[{{r}_{0}}\]  and the interatomic forces are repulsive. (b) False. As the piece of rubber returns to its original length when unloaded, it is a case of elastic hysteresis in which there is some loss of energy. This signifies non-conservative forces. (c) False. Even if the stress-strain curves are non-linear, the elastic forces are conservative as long as loading and unloading curves are identical.