A person starts his journey from centre 'O' of the park and comes back to the same position following path OPQO as shown in the figure. The radius of path taken by the person is 200 m and he takes 3 min 58 sec to complete his journey. The average speed of the person is _____________ ms^$$-$$1. (take $$\pi$$ = 3.14)

Four particles with a mass of 1 kg, 2 kg, 3 kg and 4 kg are situated at the corners of a square with side 1 m (as shown in the figure). The moment of inertia of the system, about an axis passing through the point O and perpendicular to the plane of the square, is ______________ kg m².

The excess pressure inside a liquid drop is 500 Nm^$$-$$2. If the radius of the drop is 2 mm, the surface tension of liquid is x $$\times$$ 10^$$-$$3 Nm^$$-$$1. The value of x is _____________.

Eight similar drops of mercury are maintained at 12 V each. All these spherical drops combine into a single big drop. The potential energy of bigger drop will be ____________ E. Where E is the potential energy of a single smaller drop.