Question
<p>A rock is thrown straight up from the surface of the earth. Which one of the following statements describes the energy transformation of the rock as it rises? Neglect air resistance. <br /><br />The answer is c) The kinetic energy decreases and the potential energy decreases. <br /><br />But why is this the correct answer? Could someone please explain?  This was on a quiz I took and I thought it would be the other way around as in: the kinetic energy decreases and potential energy decreases.  <br /><br /></p>
Explanation / Answer
Neither of the answers you listed are correct As the ball rises: Kinetic energy decreases and potential energy increases The instant the ball is released from the ground kinetic energy is at it's greatest, this is because K = 1/2mv2 and the velocity is miximized. As it rises, the ball's velocity is decreasing due to gravity, therefore K = 1/2mv2 has a smaller value and kinetic energy is decreasing. Conversely, potential energy, U = mgh, is 0 when the ball is released because height is equal to zero. That being said, as the ball rises the height is increasing, and therefore the value of, mgh, is increasing