Experimental design and analysis (LAB)

Finding a cart's mass from impulse

Unit 4
10 points
About 27 minutes

You can use a calculator on this question, just like on exam day.

A two-part lab question. First you design an experiment to answer a question: what you change, what you measure, the equipment and how you would analyze the data. Then you get a data table from a similar experiment, choose what to graph (often so the points fall on a straight line), plot it and use the slope, the intercept or the graph's shape to answer a question. On the exam: Question 3 of 4. Section II has 4 questions in 95 minutes (50% of the exam score), one of each type in this order; calculator allowed. The CED suggests 25–30 minutes.

The question and its sources

Students want to determine the mass of a cart without using a balance. The cart rolls on a level, low-friction track.

Part A: Available equipment

The cart, a handheld force sensor that records force versus time, a motion detector that records velocity versus time, and the track.

Source: Hypothetical lab setup

Part B: Table 1. Another group's data (each trial: the cart starts at rest and is pushed with the force sensor)

Impulse from the force–time graph J (N·s)	Final speed of the cart Δv (m/s)
0.15	0.21
0.30	0.39
0.45	0.61
0.60	0.79
0.75	1.01

Source: Hypothetical data

Suggested time: 27 minutes

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Part (A(i))

3 points

Describe an experimental procedure, using only the equipment listed, that would allow you to determine the cart's mass. Include what you would measure and how.

Your answer to part (A(i))

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Part (A(ii))

2 points

Describe how you would use your data to determine the mass of the cart.

Your answer to part (A(ii))

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Part (B(i))

1 point

Using Table 1, indicate which quantities you would graph to produce a straight line whose slope can be used to determine the cart's mass.

Your answer to part (B(i))

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Part (B(ii))

2 points

Plot the quantities you chose and draw a best-fit line. You can't draw here, so describe the graph you would draw: what goes on each axis (with units), the scale, the points you would plot (list their values), and the best-fit line.

Your answer to part (B(ii))

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Part (B(iii))

2 points

Use your best-fit line to determine the mass of the cart.

Your answer to part (B(iii))

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