4. A 15,000kg railroad car moving at 7m/s to the right collides and sticks to another railroad car with a mass of 17,000kg that is moving in the same direction at 1.5m/s.
What is the velocity of the joined cars after the collision?

they are non-matter

explanation:

they are non-matter. basically, any type of energy or any abstract concept is an example of something that does not matter. other examples include dreams, magnetism, radio, and hate

potential energy is directly proportional to height.

more height = more potential energy.

greatest increase in height = greatest increase in potential energy

where are the points with the greatest increase in height ?

has to be c-e or d-e .

the displacement produced by the body.  

the amount of force subjected to the body.  

the angle between the direction of force and displacement

the skeletons of most mammals reach a certain size and then stop growing. however, many animals, including some mammals, keep growing throughout their lives. kangaroos, for example, just keep growing and growing until they die. also, the longer an animal lives the greater the chance it might catch some deadly disease.