How far do you have to lift a 10kg bag of salt to do 250j of work?

Why are some galaxies’ spectra blueshifted rather than redshifted? question 4 options:

Why is there friction between objects

An experiment is designed to test the relationship between the initial height of a basketball before it is dropped to the height of its rebound bounce. the height of the rebound bounce is measured using a scale positioned behind the ball. in the above experiment, which condition would not be controlled? a). the starting height of the ballb). the surface the ball bounces on c). the type of ball d). the method to measure the rebound height of the ball