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Catalyst

Catalyst. There is a 300 kg roller coaster car at the top of a 30 m hill. It goes down the hill and starts coasting once it hits the bottom of the hill. What was the car’s initial PE? What was the car’s initial KE? What was the car’s final PE? What was the car’s final KE?

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Catalyst

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  1. Catalyst • There is a 300 kg roller coaster car at the top of a 30 m hill. It goes down the hill and starts coasting once it hits the bottom of the hill. • What was the car’s initial PE? • What was the car’s initial KE? • What was the car’s final PE? • What was the car’s final KE? • How fast was the car going once it started coasting at the bottom of the hill?

  2. Today’s Agenda

  3. Law of Conservation of Energy • Energy cannot be created or destroyed. • Energy can only be transferred from one form to another but the total amount never changes! PEI + KEI = PEF + KEF

  4. Conservation of Mechanical Energy • The sum of KE and PE remains constant. (Total mechanical energy is always constant.) • One type of energy changes into another type. • For the falling book, the PE of the book changed into KE as it fell. • As a ball rolls up a hill, KE is changed into PE.

  5. Kinetic and potential energy convert to one another PE max PE max no KE no KE KE max KE max no PE no PE

  6. PE KE PE KE Discussion Question a. A glass is at rest in a persons hand. The glass is then released, and falls towards the ground. What type(s) of energy does the glass have right before it is released from rest? the instant before it hits the ground? Half way down? Gravitational Potential Kinetic (motion) b.

  7. Rollercoaster Science! Have you ever been on a roller coaster that went higher on the second hill than on the first? It’s physically impossible! The roller coaster can never have more potential energy than it started with at the beginning.

  8. Problem 1 • A 7 kg crate is dropped from the top of a 40 m tall ledge and falls to the ground. • What is its initial potential energy? • What is its initial kinetic energy? • What is its final potential energy? • What is its final kinetic energy? • What is its final speed?

  9. Problem 2: Another method • A 40 kg skydiver drops from an airplane, which is 1500 m high in the air. • Find the final speed of the diver(without a parachute) right before he hits the ground.

  10. Problem 3: Another Method • A 0.2 kg water bottle was at rest on a tabletop before falling to the ground. It hit the ground with a speed of 2m/s. What was the initial height of the table?

  11. Competitive Practice • We are going to do some competitive review and practice of law of conservation of energy • One whiteboard and marker per group • Groups must rotate who writes the answer and presents it, but all group members should help solve each problem

  12. Competitive Practice 1 What type of energy does a ball rolling down a hill have?

  13. Competitive Practice 2 What type of energy does a ball have when it is thrown in the air and reaches its maximum height before coming back down?

  14. Competitive Practice 3 A 3 kg box is dropped from a tree that is 60 m tall. What type of energy does it have initially? Calculate it.

  15. Competitive Practice 4 A 30 kg boy drops from a diving board that is 15 m tall. What type of energy does it have right before it hits the ground? Calculate it. Note: Think about what your first steps need to be!

  16. Competitive Practice 5 A 3 kg bowling ball is dropped from a building that is 10 m tall. How fast is the ball going right before it hits the ground? Note: Think about what your first steps need to be!

  17. Today’s Agenda

  18. Independent Practice Complete the problems and the challenge question. Once you successfully finish those and get them checked by me, you can start working on homework • A 0.5 kg book is dropped from the top of a 50 m tall building. Calculate the speed of the book right before it hits the ground. (Remember to follow ALL Steps even if they aren’t listed – need to find initial KE first!) • A 2 kg ball starts on the ground. It is given some velocity and rolls up a hill that is 8 m tall. For the ball to reach the top of the hill, what is the initial speed it was rolled at? (Remember to follow ALL Steps even if they aren’t listed – need to find initial KE first!) CHALLENGE: A 1 kg book falls from a height of 20 m. How fast is it going when it is 3 m from the ground?

  19. Today’s Agenda

  20. Exit Slip A 300kg helicopter takes off from the ground at 5 m/s. It reaches some sort of maximum height before going back to the ground. • 1. What is the maximum height it reaches?

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