GCSE Physics (AQA)

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Conservation of Momentum Calculations

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Forces Momentum

Conservation of Momentum Calculations

9:51 Using the Conservation of Momentum
Spec 4.5.7.2
Previous Colliding & Sticking Next Colliding & Sticking Calculations
  • Conservation of momentum principle: total momentum in a closed system remains constant after a collision.
  • Equation: Total momentum before collision = Total momentum after collision.
  • Momentum calculation: Multiply velocity by mass.
  • Example with two balls: Different masses (M1, M2) and velocities (U1, U2) before collision; velocities change to V1, V2 after collision.
  • Momentum is a vector; direction matters (opposite directions result in negative values).
  • Conservation of momentum equation: M1U1 + M2U2 = M1V1 + M2V2.
  • Use the equation to find unknown velocities if masses and other velocities are known.
  • Example problem: Two trolleys with masses 0.5 kg and 0.2 kg, initial velocities 2 m/s and 1.5 m/s, respectively.
  • After collision, 0.5 kg trolley moves at 0.8 m/s; calculate velocity of 0.2 kg trolley.
  • Steps:
  • 1. Sketch and label diagram of collision.
  • 2. Calculate total momentum before collision.
  • 3. Determine total momentum after collision (same as before).
  • 4. Calculate momentum of 0.5 kg trolley after collision.
  • 5. Calculate momentum of 0.2 kg trolley after collision.
  • 6. Rearrange momentum equation to solve for velocity.
  • 7. Calculate velocity of 0.2 kg trolley (1.5 m/s, positive direction).
  • Practice is essential for mastering conservation of momentum problems.

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