Chapter 4 Energy Notes Section 4.1 The Nature of Energy A. Energy is the ability to cause change. 1. Kinetic energy – energy in the form of motion ___________ What does Kinetic mean ? xbox kinect , kinesthetic, telekinesis a. The amount of kinetic energy an object has depends on its mass and its ________________ speed b. kinetic energy = 1 /2 mass x speed 2 KE = 1/2mv2 KE = .5 X kg x v 2 c. Joule - the SI unit used to measure energy Turn over your note page & copy these examples down Title “Kinetic Math Problems” Formula KE = 1/2mv2 1. What is the KE of a 44kg cheetah running at 31 m/s? M V KE = ? M = 44 kg V = 31 m/s KE = .5 x 44 x 31 2 In the calculator always do the squaring first …… 31 x 31 = .5 x 44 x 961 KE = 21,142 J WRITE THIS DOWN ON THE BACK PAGE OF YOUR NOTES 2.Calculate the kinetic energy of a 1500 kg car moving at a speed of 18 m/s ? M V KE = 1/2 mv2 KE = ? M = 1500 kg V = 18 m/s KE = .5 x 1500 x 18 2 In the calculator always do the squaring first …… 18 x 18 = .5 x 1500 x 324 KE = 243, 000 J 2. Potential energy – energy stored in a motionless, object, giving it the potential to cause change a. Kinetic energy can become potential energy. b. Potential energy can become kinetic energy. Example: • * A ball goes up with kinetic energy, loses it, gains potential energy, slows down and falls, gains kinetic energy. 3. Elastic potential energy – energy stored by things that stretch or compress Example – spring 4. Chemical potential energy – energy stored in chemical bonds between atoms. Example – converting food into energy 5. Gravitational potential energy – energy stored by things that are above Earth. a. The amount of gravitational potential energy an object has depends on its mass, the acceleration due to gravity, and its height above ground. b. Gravitational potential energy = mass in kilograms x 9.8 m/s2 x height in meters or = mgh Turn back of your notes & write down this example M h 1. 30 kg rock climber is at a point 20 m above the base of the cliff? Solve PE? FORMULA : PE = mgh m = mass m= g= g = 9.8 m/s2 30 kg ____________ 2 9.8 m/s _________(always this number) ___ 20 m h = ____________ 5880 J PE = ____________ h = height PE = 30 x 9.8 x 20 = 5880 J Turn back of your notes & write down this example M 2. What is the kinetic energy of a 44 kg cheetah running at 31 m/s. KE = 1/2mv2 V M = __________________ 44 kg 31 m/s V = __________________ 21142 J KE = _________________ = .5 x 44 x 31 2 = .5 x 44 x 961 OPTIONAL: To write down on the back of your notes • How much kinetic energy does an object have if it’s mass is 5.0 kg and a speed of 4.0 m/s? M V KE = ½ mv2 = .5 x 5 x 4 2 =. 5 x 5 x 16 5.0 kg M = __________ 4.0 m/s V = __________ 40 J KE = ____________ = 40 J
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