Answer to Question 4 
Equation:
The angular velocity: w = 2 pf = 2 × p × 50 Hz = 314.15 rad s^{1}
We know the mass per unit length: m = 1.25 × 10^{3} kg ÷ 1.60 m = 7.8125 × 10^{4} kg m^{1}
(a) Now we can work out the power: P = 1/2 × 7.8125 × 10^{4} kg m^{1} × (2 × p × 50.0 Hz)^{2} × (20 × 10^{3} m)^{2} × 115 m s^{2} = 1.77 W = 1.8 W (2 s.f.)
(b) I = (1.77 W ÷ 2.5 V) = 0.71 A (2 s.f.)
