Momentum in two dimensions and collisionsEdexcel International A Level Physics: Flashcards
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How do you apply conservation of momentum in two dimensions?
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- How do you apply conservation of momentum in two dimensions?
- Resolve momenta into perpendicular components and conserve each component separately.
- State the condition for momentum to be conserved.
- No resultant external force acts on the system.
- What is an elastic collision?
- One in which total kinetic energy is conserved.
- What is an inelastic collision?
- One in which some kinetic energy is transferred to other forms such as thermal energy and sound.
- Is momentum conserved in an inelastic collision?
- Yes, momentum is conserved in all collisions without external forces.
- How do you decide if a collision is elastic?
- Calculate total kinetic energy before and after; equal means elastic.
- Give the formula for kinetic energy in terms of momentum.
- Ek = p²/2m.
- Derive Ek = p²/2m.
- Ek = ½mv² and v = p/m, so Ek = ½m(p/m)² = p²/2m.
- Two bodies have the same momentum. Which has more kinetic energy?
- The one with the smaller mass, as Ek = p²/2m.
- A body at rest is hit and the first object moves off at an angle. What is the total initial perpendicular momentum?
- Zero, so the final perpendicular components must cancel.
- What does ICT analysis do in Core Practical 10?
- Tracks the spheres frame by frame to give speeds and angles before and after the collision.
- Can kinetic energy be resolved into components?
- No, it is a scalar; add the total for each object.
Exam questions on Momentum in two dimensions and collisions
- On a frictionless air table a puck of mass 0.16 kg moving at 5.0 m s⁻¹ collides with an identical stationary puck. After the collision the first puck moves at 3.0 m s⁻¹ at 53° to its original direction of motion, and the second puck moves off on the other side of the original line of motion.Determine whether the collision is elastic.2 marks
- A spring-loaded plunger gives each of two trolleys, X of mass 0.50 kg and Y of mass 2.0 kg, a momentum of 3.0 kg m s⁻¹ along a frictionless track.Derive an expression for the kinetic energy of a non-relativistic particle in terms of its momentum p and mass m, and use it to calculate the kinetic energy of trolley Y.2 marks
- In Core Practical 10 a student films a ball bearing of mass 0.028 kg moving at 0.60 m s⁻¹ across a smooth table top as it collides with an identical stationary ball bearing, and uses video analysis software to measure the motion. After the collision the first ball bearing moves at 0.30 m s⁻¹ at 40° to its original direction, and the second moves off on the other side of the original line of motion.Calculate the speed and direction of motion of the second ball bearing after the collision.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).