# P2.2 Kinetic Energy

Mindmap of the topic P2.2 Kinetic energy. Comment if you have any questions :)

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- Created by: Karimoja
- Created on: 30-12-14 10:31

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- P2.2 Kinetic Energy
- Work done and Potential energy
- Work Done (J) = Force (N) X Distance (M)
- E.g. Pushing a car 50M by applying a force of 20N work done is 1000J. 20 X 50 = 1000

- Gravitational Potential Energy = Mass X gravity X height
- On Earth gravity is 10N/Kg
- A cow weighing 56kg is raised 5.2m. Graavitational Potential Energy = 56 X 10 X 5.2 = 2912J

- Work Done (J) = Force (N) X Distance (M)
- Kinetic Energy
- Kinetic Energy (J) = ½ X Mass (kg) X Speed² (m/s)
- A bike that weighs 50 kg travells at 10m/s. It's kinetic energy = ½ X 50 X 10² = 2500J

- Kinetic energy can be transferred into other types of energy like heat (friction)
- Kinetic energy lost = other energy gained

- Kinetic Energy (J) = ½ X Mass (kg) X Speed² (m/s)
- Forces and Elasticity
- Force applied = Spring Constant X extension. F= k X e
- The extension of a stretched spring is directly proportional to the force

- Any object which returns to its original shape after removing a force is elastic
- The energy used to change the shapeis stored as elastic potential energy
- This energy is then converted to kinetic when the force returns to it's original shape

- The energy used to change the shapeis stored as elastic potential energy
- There is a maximum force an elastic object can take and still extend proportionally called the limit of proportionality
- Increasing the force past this point ccauses the material to become permanently stretched

- Force applied = Spring Constant X extension. F= k X e
- Momentum
- Momentum (kg m/s)= Mass (kg) X Velocity (m/s) (speed)
- Momentum Before = Momentum After
- E.g. 2 skaters collide. Ed is 80kg and travelling at 2m/s and Sue is 60kg travelling at 1.5m/s the other way
- Total momentum before = (80 X 2) + (60 X -1.5) = 70kgm/s
- Total momentum after = 140kg X speed which must = 70. 140v = 70. V=0.5m/s

- E.g. 2 skaters collide. Ed is 80kg and travelling at 2m/s and Sue is 60kg travelling at 1.5m/s the other way

- Car safety
- Brakes reduce kinetic energy by transferring it to heat and sound energy
- Regenerative brakes store the kinetic energy from the brakes rather than wasting it

- If a car crashes a lot of kinetic energy is converted very quickly
- Crumple zones in the front and back of cars crumple on impact converting kinetic energy as shape changes
- This increases the impact time decreasing the force produced

- Side impact barsdirect energy away from passaengers
- Seatbelts sabsorb some kinetic energy by stretching
- Air bags slow you down gradually to prevent hitting hard surfaces in the car

- Crumple zones in the front and back of cars crumple on impact converting kinetic energy as shape changes

- Brakes reduce kinetic energy by transferring it to heat and sound energy
- Key Words
- Weight-A force due to gravity
- Energy-Capacity to do work
- Work-Transfer of energy
- Power-Amount of energy transferred per second (J / S)
- Momentum is a property of moving objects

- Work done and Potential energy

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