Give reason for the following
(a) Bicycle wheels are provided with spokes
(b) There are two fan a helicopter.

Explanation

With the help of spokes, the rim of the wheel in ennected to it axle and thus, the mass of the wheel wat concentrated at its rim. So, the moment of inertia of the wheel increase. The treater the moment of inertia, the more is the opposition to any change in uniform rotational motion. As result, bigyele un moothly and uniform speed is ensured.
If the halecopter has only one, fan the helicopter itself will start rotating in opposite direction to that of the relation of fan in order to regular momentum