If an object is moving at a constant speed, the forces acting on it must be another way to say this is net force =

The way the question is worded, it has no answer.

It should be: "If an object is moving at a constant velocity, ... ".

Then, the forces on it must be balanced.

Another way to say this is Net force = zero.

what experimental evidence led scientists to change from the previous model to this one?

a few of the positive particles aimed at a gold foil seemed to bounce back.

the colors of light emitted from heated atoms had very specific energies.

experiments with water vapor showed that elements combine in specific proportions.

cathode rays were bent in the same way whenever a magnet was brought near them.