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starter. My mass is about 75 kg. When I climb my stairs, I rise vertically by 3 metres. What is my weight (in newtons)? 750 N How much gravitational potential energy do I gain? 2250 J. Momentum. L.O. Calculate the momentum of a moving object.

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  1. starter • My mass is about 75 kg. When I climb my stairs, I rise vertically by 3 metres. • What is my weight (in newtons)? 750 N • How much gravitational potential energy do I gain? 2250 J

  2. Momentum L.O. Calculate the momentum of a moving object. To use the conservation of momentum to calculate the mass, velocity or momentum of a body involved in a collision or explosion.

  3. Homework: Kinetic Energy and Basic Momentum Calculations worksheet

  4. How will the truck and car move after they crash into each other?

  5. The momentum of an object = its mass x its velocity

  6. Use a calculator to work out the momentum in each of these cases: • Jack has a mass of 50 kg and runs with velocity 8 m/s. • A truck of mass 40 000 kg is travelling at 18 m/s (40 mph). • A car of mass 1000 kg is travelling at 31.6 m/s (70 mph). • A train with a mass of 120 000 kg has a velocity of 40 m/s (about 90 mph). • The Earth has a mass of 6  1024 kg and is moving around the Sun with a velocity of 30 000 m/s (about 67 000 mph). Calculate the Earth’s momentum. • A crash report says ‘The train had a momentum of 3 790 000 kg m/s.’ If the train had a mass of 120 000 kg, what was its velocity?

  7. Investigating collisions. Work out the momentum of the objects before and after the collision. Remember momentum have a direction as well as size.

  8. Momentum is conserved whenever objects interact, provided no external forces act on them.

  9. To do: Workbook page 70

  10. Momentum L.O. Calculate the momentum of a moving object. To use the conservation of momentum to calculate the mass, velocity or momentum of a body involved in a collision or explosion.

  11. Marking Homework • 1a) KE = ½mv2 = ½ x (400) x (15)2 = 45,000 J • 1b) Momentum = mv = (400) x (15) = 6,000 kgm/s • 2a) KE = ½mv2 = 1248 J • 2b) Reduced by a quarter as KE is proportional to v2. • 2c) Momentum = mv = 312 kgm/s

  12. Marking Homework 5 m/s 7 m/s • 3a) • 3b) Momentum =mv = 70x5 = 350 kgm/s • 3c) Momentum =mv = -50x5= -350 kgm/s • 3d) 350 – 350 = 0 50 kg 70 kg

  13. Marking Homework • 4a) 60,000 kgm/s • 4b) 900,000 J • 4c) 0 kgm/s • 4d) 0 J • 4e) 60,000 kgm/s • 4f) 900,000 J • 4g) 40,000 kgm/s • 4h) 400,000 J Before the crash: 30 m/s 0 m/s After the crash: 20 m/s 20 m/s

  14. Marking Homework Before the crash: 30 m/s • 4i) 20,000 kgm/s • 4j) 200,000 J • 4k) 40,000 + 20,000 = 60,000 kgm/s • 4l) 400,000+200,000 = 600,000 J • 4m) The same • 4n) Lost as heat + sound and changed into elastic potential energy in the deformed metal. 0 m/s After the crash: 20 m/s 20 m/s

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