Students in a physics lab design an experiment to determine the coefficient of static friction between a 1.8-kg jack-o'-lantern and the tabletop on which it rests. Their setup is shown in
the figure below. The basic procedure is to pour sand slowly into the pail until the pumpkin
begins to slide. The pail with the sand in it is then placed on a scale and found to weigh 11 N.
What is the coefficient of static friction between the jack-o'-lantern and the table?

a and b sometimes have a positive value

object 2 because all the other ones are wrong

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.