2018 specimen

• suggest one pro of being able to detect infrared

  -The object can be seen in the dark
• equation linking to frequency, wave speed, wavelength

  wave speed=frequency $\times$ wavelength
• 2 factors determine the momentum of the swimmer

  -mass

  -velocity
• unit of momentum

  kg m/s
• An equation links the force applied and the extension of a spring

  force=spring constant $\times$extension
• Q: Compare the properties of the waves that transmit images and noises from the monitor unit.[4 marks]

  • Light waves are transverse whereas sound waves are longitudinal.
  • Light waves travel faster than sound waves.
  • Light waves have a higher frequency than sound waves.
  • Light waves have a shorter wavelength than sound waves.
  • Light waves have oscillations perpendicular to the direction of energy transfer,whereas sound waves have oscillations parallel to the direction of energy transfer.
• Q: Use the idea of conservation of momentum to explain why the boat moves backwards.[4 marks]

  Momentum before = momentum after.

  Before diving in, the momentum of the diver and the (small) boat is zero.

  After diving, the diver has forwards momentum / momentum to the right.

  Therefore, the (small) boat has equal backwards momentum / equal momentum to the left.
• Q: The swimmer’s speed increases as she swims away from the boat. The swimmer has a top speed. Explain why.[5 marks]

  As she swims, there is a drag force.

  As speed increases, so does the drag force, so she accelerates less.

  Drag force = thrust force.

  The swimmer reaches terminal velocity.
• Explain what would happen to the spring if the student kept adding weights?[2 marks]

  The spring will be deformed because it has passed the elastic limit.
• Q: Describe how Fleming’s left-hand rule can be used to determine the direction in which the rod will move when the switch is closed, and state the direction.[4 marks]

  Thumb, index finger and third finger are held mutually at right angles.

  Index finger shows the direction of the magnetic field from North to South, third finger shows the direction of the current from positive to negative terminal.

  The thumb then shows the direction of the force acting on the copper rod.

  So the copper rod will move from left to right.