1. The equation of motion for an object of mass 0.57 kg in SHM is given by

X = 7.8 cos(7.8t) (all SI units)

What is the velocity of the object as it passes through equilibrium?

2. A spring is vertically suspended. When a mass of 0.6 kg is attached to the free end of the spring, the spring extends a length of 8 cm down to its equilibrium position. The mass is then pulled down a further 8.6 cm and released. Find the speed with which it passes through equilibrium.