If a object has a mass of 20g and a volume of 3.5cm3 what is the density

Which explanation describes the forces involved for a person to walk down the sidewalk? a. the person's feet push backward on the sidewalk; the sidewalk pushes backward on the person. b. the person's feet push forward on the sidewalk; the sidewalk does not push on the person. c. the person's feet push backward on the sidewalk; the sidewalk pushes forward on the person. d. the person's feet push forward on the sidewalk; the sidewalk pushes forward on the person.

If two parallel light rays hit a mirror, they will not be parallel to each other after they reflect.

Which is a substance that can be separated by physical means and is not the same throughout