Una rapidez de 7 mm/us es igual a: a) 7000m/s b) 70 m/s c) 7 m/s d) 0.07 m/s

For this conversion you should know that 1 meter has 1000 millimeters and that 1s equals 1000000 micro seconds, then:

7mm/us * 1m/1000mm * 1000000us/1s = 7000 m/s

The mm are canceled just like the micro seconds and the result remains in m / s .

Therefore option A is correct

A) 7000m / s

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.