In a transformer, how many turns are necessary in a 110-v primary if the 24-v secondary has 100 turns?

Transformers work due to the concept of electromagnetism. When a current is allowed to pass through a length of hollow coiled wire, it creates a magnetic field. If you imagine it, the current enters the coil, leaves at the end and turns at both opposite sides then goes back again. It is drawn in the picture. 

A transformer consists of two coils of wire called the primary coil and the secondary coil. The primary coil is connected to the power source, while the secondary coil connects the source to the load. The relationship between the number of coils (N) and the induced voltages (V) is

N₁/N₂ = V₁/V₂
The subscript 1 and 2 refers to the primary and secondary coil, respectively.

N₁/100 = 110/24
N₁ = 458 turns

Velocity is the speed of an object in a certain direction so you'd need to know speed and direction