2022

• period unit

  seconds(s)
• sound waves

  longitudinal
• equation linked to wave speed, wavelength, and frequency

  v=f$\times\lambda$
• equation linked to distance, force, work done

  W=Fs
• equation linked to distance travelled, speed and time

  distance travelled=speed $\times$time
• explain one way that the motor could be changed to increase the rate at which the coil rotates.

  -Move the coil closer to the magnet

  -increase the current in the coil
• What do the labels A and B on Figure 1 represent?Choose answers from the box.[2 marks]

  A — Rarefaction

  B — Wavelength

  
• Explain why the speed of a competitor changes during the race.

  [4 marks]

  • Competitors accelerate at the start,so speed increases.
  • Road is not flat,so speed increases going downhill.
  • Competitor goes round a bend,so speed decreases.
• The train collides with a stationary carriage on the track.Explain why the velocity of the train after the collision is less than it was before the collision.Use ideas about momentum in your answer.

  [4 marks]

  • Total momentum is conserved in the collision.
  • During the collision, the momentum of the carriage increases.
  • So the momentum of the train decreases.
  • Since momentum = mass × velocity, the train velocity decreases.
• Explain why there is a force on the wire when there is a current in the wire.[2 marks]

  There is a magnetic field due to the permanent magnets, and the current in the wire produces a magnetic field.

  04.2Explain how the direction of the force on the wire can be predicted.[3 marks]

  Use Fleming’s left-hand rule:Place first finger in direction of the field lines,place second finger in direction of current,then thumb will show direction of the force.

  
• Explain two improvements to the method the student used.[4 marks]

  1. Use flasks of the same shape and size so the surface area is the same.
  2. Use equal volumes of water because volume of water affects the rate at which the water temperature increases.

  
• The initial rate of absorption of infrared radiation by the black flask was greater than the initial rate of absorption by the white flask.How does Figure 8 show this?[1 mark]

  Black flask line has a greater gradient.
• Explain why the temperature of the water in the flasks increased and then became constant.[4 marks]

  • The flasks absorb infrared radiation and transfer energy to surroundings (by heating and emission of infrared).
  • Initially, the rate of absorption of infrared is greater than the rate of energy transfer to the surroundings (causing the temperature to increase).
  • (Rate of) energy transfer to surroundings increases as the temperature of the flasks increases.
  • Eventually, the rate of energy transfer to surroundings = rate of energy transfer to flasks (causing the temperature to become constant).
• Explain how the gradient of the line on Figure 10 shows that the resultant force on the car was not constant.[3 marks]

  • Gradient is equal to acceleration.
  • Gradient is not constant.
  • So resultant force is not constant because F=maF = maF=ma.
• In Question 07.2 it was assumed that the acceleration was a constant 9.8 m/s².Evaluate this assumption.

  [4 marks]

  • As the apple falls, air resistance increases.
  • So resultant force decreases.
  • So acceleration will decrease.