The velocity of a wave is primarily determined by the

The propagation velocity of a wave depends on the medium in which it propagates.  

In addition, it depends on the type of wave, for example a mechanical or electromagnetic wave.  

In any case, the velocity of a wave is generally related to the value of the wavelength and the period, and can be expressed mathematically through the following formula:  

where is the velocity of the wave, is the wavelength and is the period.

Therefore:

a small object of mass 3.66 g and charge -17.6 µc is suspended motionless above the ground when immersed in a uniform electric field perpendicular to the ground. what are the magnitude and direction of the electric field?