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Calculating Energy

Energy is defined as the ability to cause change. Energy can cause changes in motion and positions of objects. Thus when you do work on an object, you are giving that object energy. Therefore energy and work are both measured in units called Joules (J). 1 J = 1 N-m

Kinetic energy is defined as energy in the form of motion, or in use. Two factors that determine the amount of kinetic energy an object have are mass and speed. The more massive an object is, the more kinetic energy it has, and the more speed an object has, the more kinetic energy it has. Mass is proportional to kinetic energy. This means that if mass is doubled, KE is also doubled. Speed in not proportional, meaning that when speed doubles, KE quadruples. Therefore we can calculate kinetic energy with the following equation:

KE = ½ mass X speed2

Potential energy is defined as energy of position or condition. This energy is often referred to as stored energy. Gravitational potential energy is dependent upon the force (weight) of an object due to its height (position above the Earth). We can calculate the amount of gravitational potential energy of an object with the following equation:

GPE = weight X height

Directions: Use the above equations to calculate the amount of energy in each situation. Show your work by writing the equation, placing the numbers in the equation, and circling your answer with the correct units.

  1. What is the kinetic energy of a car that has a mass of 1200 kg and is moving at a speed of 20 m/s? (3 points)
  1. What is the kinetic energy of a car that has a mass of 2400 kg and is moving at 20 m/s? How does the kinetic energy of this car compare to the kinetic energy of the previous example? (4 points)
  1. What is the kinetic energy of a 4000 kg elephant that is running at 2 m/s? at 4 m/s? How do the two kinetic energies compare with one another? (6 points)
  1. What is the kinetic energy of a 2000 kg bus that is moving at 30 m/s? (3 points)
  1. What is the kinetic energy of a 3000 kg bus that is moving at 20 m/s? (3 points)
  1. What is the gravitational potential energy of a cat that weighs 40 N standing on a table that is 0.8m above the ground? (3 points)
  1. What is the gravitational potential energy of a diver who weighs 500 N standing on a platform that is 10 m off the ground? (3 points)
  1. What is the gravitational potential energy of a diver who weighs 600 N standing on a platform that is 8 m off the ground? (3 points)
  1. A woman weighing 70 N prepares to bungee jump off a bridge. If the bridge is 200 meters high, how much potential energy (J) does the woman have? (3 points)
  1. A boulder weighing 500 N teeters on the edge of a 100 m high cliff. What is its potential energy (J)? (3 points)
  1. A man weighing 100 N prepares to skydive from a plane. If he has a potential energy of 350,000 J, how high above the ground is the plane? (3 points)