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Conservation of Momentum: Calculations and Principles

Learn how to apply the equation p=mv to find momentum, velocity, and mass of objects, as well as how conservation of momentum can be used to find velocities. Practice a range of calculations involving object velocities.

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Conservation of Momentum: Calculations and Principles

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  1. Baseline (Aiming for 4): Apply the equation p=mv to find the momentum, velocity and mass of an object. Further (Aiming for 6): Describe how the principal of conservation of momentum can be used to find the velocities of objects. Challenge (Aiming for 8): Apply the principals of conservation of momentum to a range of calculations involving the velocities of objects.

  2. Conservation of momentum • In a closed system, the total momentum before an event and the total momentum after an event are the same. This is called conservation of momentum. • Events you may be asked about in your exams are: • Collisions • Explosions

  3. Momentum is conserved in any collisionor explosion, providing no externalforces act on the objects. Conservation of Momentum The Law of Conservation of Momentum states that: In a closed system, where no external forces act: • The total momentum before the collision is equal to the total momentum after the collision. • If one object loses momentum, the other object must gain the same amount of momentum.

  4. Example question M= 1Kg M= 1Kg Two trolleys of identical mass, 1Kg, are stationary. They are fired away from each other in an explosion. • What is the total momentum of both trollies before the explosion? • If the first trolley is pushed to the left as shown above, draw an arrow to show the direction of travel of the second trolley. • If The first trolley travels away at 5m/s calculate its momentum. • If the total momentum is conserved, what is the momentum of the second trolley? • Calculate the velocity of the second trolley. p=mv p=1x0 p= 0 kg m/s p=mv p=1x5 p= 5 kg m/s If the total momentum must remain 0, then the second trolley must have a momentum of -5 kg m/s v = p ÷ m v= -5 ÷ 1 v = -5 m/s

  5. Example question M= 1Kg M= 2Kg Two trolleys with different masses are stationary. They are fired away from each other in an explosion. • What is the total momentum of both trollies before the explosion? • If the first trolley is pushed to the left as shown above, draw an arrow to show the direction of travel of the second trolley. • If The first trolley travels away at 5m/s calculate its momentum. • If the total momentum is conserved, what is the momentum of the second trolley? • Calculate the velocity of the second trolley. p=mv p=1x0 p= 0 kg m/s p=mv p=1x5 p= 5 kg m/s If the total momentum must remain 0, then the second trolley must have a momentum of -5 kg m/s v = p ÷ m v= -5 ÷ 2 v = -2.5 m/s

  6. Challenge question The figure to the left shows a skateboarder jumping forwards off his skateboard. The skateboard is stationary at the moment the skateboarder jumps. The mass of the skateboard is 1.8 kg and the mass of the skateboarder is 42 kg. Calculate the velocity at which the skateboard moves backwards if the skateboarder jumps forwards at a velocity of 0.3 m / s. Velocity of skateboard = ........................................ m / s (3)

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