Q22 · 2024 · Paper 1Simple familiar5 marks
QUESTION 22 (5 marks)
Special relativity accounts for the observation that more muons from cosmic rays are detected near Earth’s surface than expected. Explain this phenomenon by outlining why Newtonian physics cannot explain this scenario while special relativity can. Refer to the frames of reference of both the travelling muons and the observer near the Earth’s surface.
WORKED SOLUTION
5 marksQCAA guide · typeset solution
ANSWER
See worked solution below.
Worked solution
Since muons are short-lived particles, they shouldn’t reach the
Earth’s surface according to Newtonian physics.
But muons travel at close to the speed of light. As muons enter
the atmosphere, an observer external to the particles’ frame of
reference will witness them existing longer than expected due to
time dilation. Muons experience length contraction, so they can
travel further than predicted by Newtonian physics.
• identifies that muons have a very short half-
life [1 mark]
• explains that muons are unlikely to reach
Earth’s surface using Newtonian physics
[1 mark]
• identifies that muons travel at relativistic
speeds [1 mark]
• explains that from the observer’s frame of
reference, the muon’s half-life will be longer
due to time dilation [1 mark]
• explains that from the muon’s frame of
reference, it experiences length contraction
[1 mark]
One QCAA sample method typeset for web; criterion wording is adapted from the official marking guide.
How many marks did you earn?
Compare your working with the guide above.