1. Direct evaporation from water bodies like, sea, rivers, and oceans 2. Moisture from the land (you must have seen land dries out) 3. Moisture from the plant (small capillaries from the plants sucks water from the land and goes to atmosphere in form of vapour from leaves,).
The radial force on the particle is given by the Lorentz force. They don't give you the velocity so you have to solve for it in terms of the radius and get them to cancel.
Newton's First Law states that an object would remain at rest or in uniform motion in a straight line unless an unbalanced force acts upon it. So the speed would be the one that remains constant.