DP Physics (first assessment 2025)

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Question 22N.1A.SL.TZ0.10

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Date November 2022 Marks available [Maximum mark: 1] Reference code 22N.1A.SL.TZ0.10
Level SL Paper 1A Time zone TZ0
Command term Question number 10 Adapted from N/A
10.
[Maximum mark: 1]
22N.1A.SL.TZ0.10

Three samples of the same liquid are mixed in an insulated container. The masses and initial temperatures of the samples are:

What is the equilibrium temperature of the mixture?


A.  45 °C

B.  36 °C

C.  30 °C

D.  24 °C

[1]

Markscheme

B

Examiners report

The same fraction of correct answers as in HL question 1, but a much higher discrimination index. Mixing three different samples is a relatively challenging problem to solve in exam conditions, but complicated algebra can be avoided by considering only two samples mixed initially before adding the last one. This strategy helps eliminate incorrect alternatives without computing the exact answer.

For example, the mixture of samples 1 and 2 would have a temperature of 45 °C (halfway between 30 and 60 °C) and adding colder sample 3 to it would have brought the temperature below 45 °C (alternative A eliminated). Similarly, the mixture of 1 and 3 has a temperature greater than 30 °C (because sample 1 has a greater mass), and adding sample 2 to it will still keep the final temperature above 30 °C (alternatives C and D eliminated, thus only B remains).

Syllabus sections