What was his starting velocity???

Vo = 18.3 [m/s]

Explanation:

To solve this problem we must use the following equation of kinematics.

Vf = final velocity = 0 (the bike stops)

Vo = initial velocity [m/s]

a = desacceleration = 6.42 [m/s²]

t = time = 2.85 [s]

Note: the negative sign in the above equation means that the motorcyclist decrease his velocity.

0 = Vo - (6.42*2.85)

Vo = 18.3 [m/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.