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QOD 97

QOD 97. Explain what it means when an object accelerates at a rate of 2 m/s 2 ? When an object accelerates at a rate of 2 m/s 2 it means that every second, the speed increases by 2 m/s. QOD 97. 4-22-14. 1. Explain what it means when an object accelerates at a rate of 2 m/s 2 ?

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QOD 97

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  1. QOD 97 Explain what it means when an object accelerates at a rate of 2 m/s2? When an object accelerates at a rate of 2 m/s2 it means that every second, the speed increases by 2 m/s.

  2. QOD 97 4-22-14 1. Explain what it means when an object accelerates at a rate of 2 m/s2? When an object accelerates at a rate of 2 m/s2 it means that every second, the speed increases by 2 m/s. 2. What is the acceleration of a cheetah that is running a velocity of 28 m/s and slows down to 20 m/s after 10 seconds? (Write equation & show steps) a = vf – via = 20 m/s – 28 m/s = - .8 m/s t10 s 10 s a = - 0.8 m/s2

  3. Go over answers to finding acceleration

  4. Calculating Potential & Kinetic Energy Potential Energy – stored energy of an object due to its state or position Kinetic Energy – energy of a moving object Unit – Joules (J)

  5. 1 Joule of Energy … • the energy required to lift a small apple (with a mass of approximately 100 g) vertically through one meter of air. • the energy released when that same apple falls one meter to the ground. • the kinetic energy of a 50 kg human moving very slowly (0.2 m/s).

  6. (Gravitational) Potential Energy PE = mgh Mass(kg) x Gravity x Height(m) = ___ Joules (J) Acceleration due to Gravity = 9.8 m/s2

  7. Ex: 1 A box that has a mass of 2.5 kg is sitting on a shelf that is 2 meters high. What is the gravitational potential energy of the box? • Mass = 2.5 kg • Gravity = 9.8 m/s2 • Height = 2 m PE = mgh PE = 2.5 kg x 9.8 m/s2 x 2 m = PE = 49 Joules (J)

  8. Ex: 2 A boy has a mass of 55 kg. He climbs 12 meters up a tree. What is his gravitational potential energy? • Mass = ________ • Gravity = ________ • Height = _______ PE = 6,468 Joules 55 kg 9.8 m/s2 12 m PE = mgh PE = 55 kg x 9.8 m/s2 x 12 m =

  9. Ex: 3 Find the gravitational potential energy of a pencil sitting on the edge of a desk. The pencil is 0.25 kg and the desk is 0.78 m high. PE = mgh PE = .25 kg x 9.8 m/s2 x .78 m = PE = 1.911 J

  10. Ex: 3 - challenge Find the gravitational potential energy of a pencil sitting on the edge of a desk. The pencil is 25 g and the desk is 78 cm high. Convert 25 g to ____ kg Convert 78 cm to ____ m PE = mgh PE = .025 kg x 9.8 m/s2 x .78 m = PE = 0.191 J .025 .78

  11. Kinetic Energy KE = 0.5xmv2 0.5 x Mass(kg) x Velocity(m/s) 2 = ___ Joules

  12. Ex4: Determine the kinetic energy of a 55 kg woman running with a speed of 3.87m/s. KE = 0.5 x mv 2 KE = 0.5 x 55 x (3.87) 2 KE = 0.5 x 55 x 14.97 KE = 411.9 Joules

  13. Ex5: What is the kinetic energy of a cheetah with a mass of 72 kg running a speed of 29 m/s. KE = 0.5 x mv 2 KE = 0.5 x 72 x (29)2 KE = 0.5 x 72 x 841 KE = 30,276 Joules

  14. Ex6: What is the kinetic energy of a pencil with a mass of 0.25 kg thrown a speed of 10 m/s. KE = 0.5 x mv 2 KE = 0.5 x 0.25 x (10)2 KE = 0.5 x 0.25 x 100 KE = 12.5 Joules

  15. Practice WS

  16. Ex 4: (Create your own problem!) • With your partner, write a word problem that tells the mass and height of your object/person. • Draw a simple diagram of your word problem. • Solve your problem to find the gravitational potential energy of your object/person, but don’t write down the answer! • Pass the problem to your neighbors to solve.

  17. KE = ½ x mass x velocity

  18. Take Pictures!! • With a partner… • Take 3 pictures of kinetic energy • At least 1 must include a person • Take 3 pictures of potential energy • At least 1 must include a person

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