Mass, length and time are all SI base quantities. A wire hangs between two fixed points, as shown in Fig. 1.1. [Figure 1.1] A child's swing is made by connecting a car tyre to the wire using a rope and a hook. The system is in equilibrium with the wire hanging at an angle of 17° to the horizontal. The tension in the wire is 150 N. Assume that the rope and hook have negligible weight. The wire has a cross-sectional area of 7.5mm² and is made of metal of Young modulus 2.1 x 10¹¹ Pa. The wire obeys Hooke's law.