An object is hanging by a string from the ceiling of an elevator. the elevator is slowing down while moving upward.

what is the magnitude of the tension in the string?

The magnitude of the tension is less than the object's weight

Explanation:

As per the question:

From Fig. 1

The forces and the acceleration are shown in the figure

Since, the elevator slows down in its upward motion, this means that the final velocity is less than the initial velocity and the elevator decelerates.

Therefore, we take the acceleration as negative, '- a'.

Thus

Balancing the forces:

T - mg = m(- a)

T = mg - ma = m(g - a)

Thus it clearly shows T < mg

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.