A research vessel moves at a constant speed through still water. A sound source fixed to the vessel emits a steady frequency. Detector A is stationary in the water ahead of the vessel, and detector B is stationary behind it.
Which statement about the detector readings is correct?
A records more wave crests each second than B, because the crests reaching A are closer together.
A records more wave crests each second than B, because the source emits more crests towards A.
A and B record the same number of wave crests each second, because the source frequency is steady.
B records more wave crests each second than A, because the vessel is moving away from B.
94 exam-style questions on Edexcel GCSE Physics 7.2 The Universe and red-shift, covering 7.2.1 Big Bang and Steady State theories, 7.2.2 Evidence for the Big Bang, 7.2.3 The Doppler effect and red-shift, 7.2.4 Red-shift as evidence for an expanding Universe, and 7.2.5 The CMB and the accepted model. Each one has a worked solution and a mark scheme showing where the marks go.