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Understanding Weight, Energy, and Momentum: Key Concepts in Physics

Dive into the fundamental concepts of physics with this comprehensive overview on weight, gravitational potential energy, and momentum. Learn how to calculate your weight in newtons and the energy gained from climbing stairs, along with the conservation of momentum in collisions. Explore examples involving various objects, including vehicles and the Earth, and master the fundamental formulas needed to compute kinetic energy and momentum. This resource is designed for students looking to enhance their understanding of these essential physical principles.

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Understanding Weight, Energy, and Momentum: Key Concepts in Physics

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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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