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Do now!

He’s going to blow!. Be careful. Neutral. Good. Excellent. MOODOMETER. How much energy sort ?. Do now!. Today’s lesson. Calculating Gravitational Potential energy Calculating kinetic energy. A reminder. Energy cannot be made or destroyed, only transformed (changed).

jonah-contreras
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Do now!

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  1. He’s going to blow! Be careful Neutral Good Excellent MOODOMETER How much energy sort ? Do now!

  2. Today’s lesson • Calculating Gravitational Potential energy • Calculating kinetic energy

  3. A reminder • Energy cannot be made or destroyed, only transformed (changed). • Energy is measured in Joules. That’s me!

  4. Types of Energy Heat Chemical Light Gravitational Sound Elastic/strain Kinetic Nuclear Electric Stored/potential

  5. Gravitational potential energy Ep = mgh m kg J N/kg or m/s2 Can you copy this please? We will learn in later lessons where this formula comes from.

  6. Example Woof! (help!) A dog of mass 12 kg falls from an aeroplane at a height of 3.4 km. How much gravitational energy does the dog have as it leaves the aeroplane?

  7. Example On earth g = 10 m/s2 Mass of dog = 12 kg Height = 3.4 km = 3400 m

  8. Example On earth g = 10 m/s2 Mass of dog = 12 kg GPE of dog = mgh = 12 x 10 x 3400 = 408 000 J Height = 3.4 km = 3400 m

  9. Example GPE of dog = mgh = 12 x 10 x 3400 = 408 000 J Just before the dog hits the ground, what has this GPE turned into?

  10. Kinetic energy

  11. Kinetic energy Kinetic energy of an object can be found using the following formula Ek = mv2 2 where m = mass (in kg) and v = speed (in m/s)

  12. Example A bullet of mass 150 g is travelling at 400 m/s. How much kinetic energy does it have?

  13. Example A bullet of mass 150 g is travelling at 400 m/s. How much kinetic energy does it have? Ek = mv2/2 = (0.15 x (400)2)/2 = 12 000 J

  14. Energy changes

  15. Example GPE of dog = mgh = 12 x 10 x 3400 = 408 000 J Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

  16. Example GPE of dog = mgh = 12 x 10 x 3400 = 408 000 J KE at bottom = 408 000 J Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

  17. Example GPE of dog = mgh = 12 x 10 x 3400 = 408 000 J KE at bottom = 408 000 J = mv2/2 Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

  18. Example 408 000 = mv2/2 Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

  19. Example 408 000 = mv2/2 2 x 408 000 = 12 x v2 Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

  20. Example 408 000 = mv2/2 2 x 408 000 = 12 x v2 816000 = 12v2 Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

  21. Example 408 000 = mv2/2 2 x 408 000 = 12 x v2 816000 = 12v2 68000 = v2 Just before the dog hits the ground, what has this GPE turned into? Kinetic energy

  22. Example 408 000 = mv2/2 2 x 408 000 = 12 x v2 816000 = 12v2 68000 = v2 261 = v v = 261 m/s Assuming no energy is lost as air resistance – in reality the dog would have reached TERMINAL VELOCITY

  23. Let’s try some questions! Stick them in first!

  24. Homework Due next Thursday 14th April Finish ALL questions on Kinetic and Gravitational energy

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