A student tests the return spring in a door closer by applying the same force several times. The measured extensions are 31 mm, 33 mm and 45 mm. The last result is identified as anomalous. The student checks the apparatus, finds no fault and repeats the measurements, obtaining 32 mm, 31 mm and 33 mm.
Which is the best next step?
Calculate the mean of the five readings that are not anomalous.
Use only the smallest reading because it is least affected by the anomaly.
Calculate the mean of only the three readings taken after the check.
Calculate the mean of all six readings, including the anomalous result.
102 exam-style questions on Edexcel GCSE Physics 15.1 Forces and springs, covering 15.1.1 Elastic and inelastic distortion, 15.1.2 The spring constant, 15.1.3 Work done in stretching a spring, and 15.1.4 Linear and non-linear force–extension. Each one has a worked solution and a mark scheme showing where the marks go.