Comparison questions

Hey I need a hand with how to word questions in the mechanics paper that include things like a speed/time graph with two lines and it asks you to compare the speed of the lines in each section

Hi Holly,

Welcome to StudyIt.

There would normally be a term of reference used in the question, such as section B and section C. Use those terms to identify which line you are referring to.

For a speed time graph, determining the higher speed between two sections would just require you to look at which horizontal line is higher. Here is how I would word an answer:

In the speed-time graph example below you can see Bird A has a higher top speed (10 m/s) than Bird B (9m/s)

You may be asked to compare the acceleration on a speed-time graph. In this case a steeper line shows a higher acceleration. In the graph above, Bird B has a higher initial acceleration than Bird A, as the red line is steeper than the blue line. We could calculate the acceleration using:

For example, in the first three seconds, Bird B has a change in speed of 9 m/s. Its acceleration is 9 / 3 = 3 ms^-2

In a distance time graph, the steepness of the line now indicates speed. This is why it is so important to carefully check which type of graph you’re dealing with. An example answer might be worded like this:


The speed in section C-D is greater than the speed in A-B, as the gradient from C-D is steeper. The speed in B-C is zero as the distance is not changing.

I hope that helps. You can see some other examples of a speed-time graph and a distance-time graph, discussed in our earlier webinar.

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