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Question 19M.3.SL.TZ1.1a.i

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Date May 2019 Marks available [Maximum mark: 3] Reference code 19M.3.SL.TZ1.1a.i
Level SL Paper 3 Time zone TZ1
Command term Calculate Question number a.i Adapted from N/A
a.i.
[Maximum mark: 3]
19M.3.SL.TZ1.1a.i

In an experiment to measure the acceleration of free fall a student ties two different blocks of masses m1 and m2 to the ends of a string that passes over a frictionless pulley.

The student calculates the acceleration a of the blocks by measuring the time taken by the heavier mass to fall through a given distance. Their theory predicts that  a = g m 1 − m 2 m 1 + m 2 and this can be re-arranged to give  g = a m 1 + m 2 m 1 − m 2 .

In a particular experiment the student calculates that a = (0.204 ±0.002) ms–2 using m1 = (0.125 ±0.001) kg and m2 = (0.120 ±0.001) kg.

(a.i)

Calculate the percentage error in the measured value of g.

[3]

Markscheme

error in m1 + m2 is 1 % OR error in m1 − m2 is 40 % OR error in a is 1 % ✔

adds percentage errors ✔

so error in g is 42 % OR 40 % OR 41.8 % ✔

Allow answer 0.42 or 0.4 or 0.418.

Award [0] for comparing the average value with a known value, e.g. 9.81 m s-2.

Examiners report

Atwoods machine a) is a quite straightforward question that tests the ability to propagate uncertainties through calculations. Almost all candidates proved the ability to add percentages or relative calculations, however, many weaker candidates failed in the percentage uncertainty when subtracting the two masses.

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