Net force acting on a object is given by the product of its mass and acceleration. That is F = ma.
Here, the bus is moving with uniform velocity. That means acceleration of the bus is 0.
Thus net force acting on it = 2000×0 = 0 N
Note: The net force is given by F=ma. (which is 0 in this case). But there are forces acting on the bus which are not zero. Like weight of bus, normal force from road, friction force, pull of engine, air drag etc. But their sum is zero.