Which diagram correctly demonstrates the various forces acting on a ball moving horizontally with some speed?
The one showing 4 equal arrows on opposite directions.
When the ball is moving with constant velocity,it is in both horizontal as well as vertical equilibrium.
So all 4 forces acting on it must balance each other.
The one acting vertically downwards is its weight,which is being balanced by normal force due to the ground.
And horizontally acting external force is being balanced by kinetic frictional force.