An example of a substance with a definite volume and a definite shape is
a. a steel beam.
b. melted ice cream.
c. a helium balloon rising.
d. electrons in a cloud surrounding an atomic nucleus

Aballet student who learns with the of his instructor is demonstrating learning.

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.

The boy of mass 30 kg is at r1= 2 meters from the fulcrum. of the girl is 45 kg, at what r2 must she sit so that they are balanced ?