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Momentum

Momentum. Definition Problems. Mass. Weight. Weight (measured in Newtons) is the force of gravity acting on an object. Mass (e.g. in Kg) is the ‘ quantity of matter’. E.g an apple’s mass may be 0.1 kg - irrespective of gravity. It’s weight is ~ 1 N (on Earth)

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Momentum

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  1. Momentum Definition Problems

  2. Mass Weight Weight (measured in Newtons) is the force of gravity acting on an object Mass (e.g. in Kg) is the ‘quantity of matter’ E.g an apple’s mass may be 0.1 kg - irrespective of gravity It’s weight is ~ 1 N (on Earth) (or about 0.17 N on the moon)

  3. Momentum The same momentum Is a measure of the wumpf/ impact/ energy an object has It is defined as the object’s velocity multiplied by its mass momentum = velocity x mass E.g a 5 kg ball at 10 ms-1 momentum = 5 kg x 10 ms-1 = 50 kg ms-1 Double the momentum E.g a 10 kg ball at 10 ms-1 momentum = 10 kg x 10 ms-1 = 100 kg ms-1 E.g a 5 kg ball at 20 ms-1 momentum = 5 kg x 20 ms-1 = 100 kg ms-1

  4. Momentum examples Suppose a footballer delivers the same amount of wumpf in each kick He kicks a 1 kg ball at 8 ms-1 How fast would a 2 kg ball go? momentum of ball = velocity x mass = 8 ms-1 x 1kg = 8 kg ms-1 momentum of 2kg ball is same 8 kg ms-1 = velocity x 2 kg velocity = 8  2 = 4ms-1 If a ball was going 10 ms-1, what was it’s mass? momentum = 8 kg ms-1 = 10 ms-1 x mass mass = 8  10 = 0.8 kg

  5. Bounce Stick Move in same direction (difference velocities) The Principle of Conservation of Linear Momentum When 2 bodies collide 4 ms-1 8 ms-1 2 kg 3 kg The total momentum before = the total momentum after The action will depend on their velocities, masses and types of materials What might happen ?

  6. The Principle of Conservation of Linear Momentum When 2 bodies collide W1 ms-1 V1 ms-1 m kg n kg The total momentum before = the total momentum after mV1 + nW1 = mV2 + nW2 W2 ms-1 V2 ms-1 m kg n kg

  7. Conservation of Momentum - example 1 Negative - to indicate they are in opposite directions Zero - because it is stationary 4 ms-1 8 ms-1 2 kg 3 kg The total momentum before = the total momentum after If the blue ball is stationary after impact, what is happening to the red ball? total momentum before = blue momentum + red momentum =8 x 2+ -4 x 3 = 16 + -12 = 4 kg ms-1 total momentum after = 8 x 0+ Vr x 3 = 3 Vr The total momentum before = the total momentum after 4 = 3 Vr So, Vr = 4/3 = 1.33 ms-1 (i.e. to the right)

  8. Conservation of Momentum - example 2 2 ms-1 6 ms-1 BEFORE COLLISION 5 kg 25 kg V ms-1 0.4 ms-1 AFTER COLLISION 5 kg 25 kg total momentum before = blue momentum + red momentum =6 x 5+ 2 x 25 = 30 + 50 = 80 kg ms-1 total momentum after = 5 x -0.4+ V x 25 = 25V -2 The total momentum before = the total momentum after 80 = 25V - 2 25V = 82 V = 3.28 ms-1

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