Conservation of Energy and Momentum

1. Conservation of Energy and Momentum Physics 6(D)

2. Learning Objectives • Demonstrate the laws of conservation of energy and momentum in one dimension • Apply the laws of conservation of energy and momentum in one dimension • Conservation of Energy and Momentum

3. Kinetic energy (KE ) – the energy an object has due to motion • Dependent on mass (m ) and velocity (v ) • Gravitational potential energy (PEg) – the energy an object has due to its position • Dependent on mass (m ), height above ground (h), and acceleration due to gravity (g = 9.8 m/s2 ) • Law of conservation of energy – states that when no external work is done on a system, the total mechanical energy is conserved • Law of Conservation of Energy

4. Ex) Consider a sled going down a snowy hill. Assume there are no external forces at work. (a) Where will the sled have the most potential energy? (b) Where will the sled have the most kinetic energy? (c) Where will the sled have the most mechanical energy? • Conservation of Energy Conceptual Example

5. Conservation of Energy Calculation • Write unknown and givens • Identify the formula and rearrange, if needed Ex) If the sled in the previous problem starts from rest and travels down a hill that is 17 m high, what is the final velocity of the sled? • Convert units and find intermediates, if needed • Plug in and solve • Make sure the answer is reasonable

6. Conservation of Energy Calculation • Write unknown and givens • Identify the formula and rearrange, if needed Ex) A bowling ball starts from rest and is rolled down a hill. When the bowling ball reaches the ground, it is moving at 13 m/s. What is the height of the hill? • Convert units and find intermediates, if needed • Plug in and solve • Make sure the answer is reasonable

7. Momentum ( p ) – the product of an object’s mass (m ) and its velocity (v ) • Law of conservation of momentum – states that the total momentum of a system before a collision is equal to the total momentum after the collision • Law of Conservation of Momentum

8. Ex) A waiter moving to the left with 150 of momentum runs into a hostess moving to the right with 120 of momentum. What is the combined momentum of the two people after the collision? • Conservation of Momentum Example • Write unknown and givens • Identify the formula and rearrange, if needed • Convert units and find intermediates, if needed • Plug in and solve • Make sure the answer is reasonable

9. Write unknown and givens • Identify the formula and rearrange, if needed • Conservation of Momentum Example Ex) A 4,500 kg truck traveling at 25 m/s runs into a 270 kg golf cart parked on the side of the road. If the final velocity of the golf cart is 12 m/s, what is the final velocity of the truck? • Convert units and find intermediates, if needed • Plug in and solve • Make sure the answer is reasonable

10. Conservation of Momentum Example • Write unknown and givens • Identify the formula and rearrange, if needed Ex) An astronaut with a mass of 95 kg floating away from the space station can throw an object in the opposite direction to propel herself back. If the astronaut wants to move with a velocity of 1.5 m/s and can throw an object with a velocity of 15 m/s, how much mass would she need to throw? • Convert units and find intermediates, if needed • Plug in and solve • Make sure the answer is reasonable

11. Learning Objectives • Demonstrate the laws of conservation of energy and momentum in one dimension • Apply the laws of conservation of energy and momentum in one dimension • Conservation of Energy and Momentum