A 2.5 kg ball moving at 4.2 m/s collides with a 2.5 kg stationary ball in a perfectly elastic collision. What is the velocity of the second ball after the collision?

If the chemical properties of a substance remain unchanged and appearance or shape of a substance changes it is called a ?

Ahanging spring stretches by 35.0 cm when an object of mass 450 g is hung on it at rest. in this situation, we define its position as x = 0. the object is pulled down an additional 18.0 cm and released from rest to oscillate without friction. what is its position x at a moment 84.4 s later? express your answer in cm.

The amount of potential energy possessed by an elevated object is equal to what?