Which model of the solar system best supports retrograde motion of the planets?

a) ptolemy's model

b) the heliocentric model

c) an earth-centered model

Define conservation of energy in your own words be as specific as you can

When the velocity of an object is doubled, by what factor is its momentum changed? by what factor is its kinetic energy changed? a) the momentum is zero. b) the momentum is not zero. c) difficult to say.

How many seconds does it take a pebble released from rest off a bridge to fall 29.4 m ? what is the pebble's speed when it has fallen 29.4 m ?