(a) State Hooke's Law. (b) For forces up to 120 N, a spring obeys Hooke's Law. A force of 120 N causes an extension of 64 mm. (i) On Fig. 2.1. draw the force-extension graph for the spring for loads up to 120 N. 150- force/N 100- 50- 0- 20 40 Fig. 2.1 60 extension/mm 80 (ii) Calculate the spring constant & of the spring. (c) A student makes a spring balance using the spring in (b). The maximum reading of this balance is 150 N. The student tests his balance with a known weight of 140 N. He observes that the reading of the balance is not 140N. Suggest and explain why the reading is not 140 N.