# kepe - Kinetic Potential Energy Kinetic Energy Potential...

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Kinetic Energy Potential Energy Kinetic Energy You’ve probably heard of kinetic energy in previous courses using the following definition and formula… Any object that is moving has kinetic energy. E k = ½ m v 2 E k = kinetic energy (J) m = mass (kg) v = velocity (m/s) We’re going to keep on using that basic formula, but we do need to clear up the definition a little bit. What is “any object”? “Any object” just refers to anything that we can measure as having a mass . This covers everything from small subatomic particles like electrons all the way up to galaxies. When they say “moving” we need to ask “Moving relative to what?” Right now you’re sitting motionless at a computer screen, so you have no kinetic energy, right? This is true relative to the reference frame of the room you’re in. Isn’t the earth spinning on its axis? Isn’t the whole planet moving around the sun? You need to make sure that you are always sure about what your measurements are being taken in relation to. Most of the time we measure stuff relative to the surface of the earth, so things are easier, but be careful. Example 1 : A pop can with a mass of 312g is sitting in the cup holder of my car as I drive down Yellowhead at 68 km/h. a) Determine how much kinetic energy it has relative to me in the car. E k = ½ mv 2 But relative to me the pop can’s velocity is zero, so… E k = 0 J 10/21/2005 © studyphysics.ca Page 1 of 5

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b) Determine how much kinetic energy it has relative to someone standing on the side of the road. E k = ½ mv 2 = ½ (0.312 kg) (19 m/s) 2 E k = 56 J Also, be ready to manipulate this formula to solve for other variables… Example 2 : Determine the velocity of a 150 kg cart if it has 3.60e4J of kinetic energy. First, see if you can correctly solve the formula for “v”. This is one of the manipulations that
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kepe - Kinetic Potential Energy Kinetic Energy Potential...

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