When should a bar graph be used?
  a.  when the independent variable is continuous and does not show a relationship to the dependent variable.  b.  when the independent variable is continuous and shows a causal link to the dependent variable.  c.  when there is no independent variable.  d.  when the independent variable is composed of categories and does not show a relationship

If a spring has a k value of 100 newtons per meter and it is stretched 0.50 meters, what is the restoring force of the spring?

What would be the strength of earth's gravitational field at a point where an 80.0 kg astronaut would experience a 80% reduction in weight

Large electric fields in cell membranes cause ions to move through the cell wall. the field strength in a typical membrane is 1.0 x 10 7 n/c. what is the magnitude of the force on a calcium ion with charge +e? what is its acceleration? is it possible for a particle with the same charge as as calcium to have a different acceleration if placed at this location? what would change the acceleration: mass of the particle? diameter of the particle?