Afalling object that weighs 12 n encounters 3 n of upwards air resistance. what is the size of the net force on the object?

Assume the downward direction is positive and upward direction is negative

W = weight of the object = 12 N

f = air resistance on the object = - 3 N

F = net force on the object

net force is the sum of forces acting on the object , hence the net forces is given as

net force = sum of forces

F = W + f

F = 12 + (- 3)

F = 12 - 3

F = 9 N

hence the size of net force on the object comes out to be 9 N

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.