Here's why:

* MKS stands for meter-kilogram-second, which is a system of units used in physics.

* Velocity is the rate of change of an object's position with respect to time.

* Meters (m) is the MKS unit for distance.

* Seconds (s) is the MKS unit for time.

Therefore, velocity, which is distance divided by time, is expressed in meters per second (m/s) in the MKS system.