Experimental design and analysis (LAB)

Finding the coefficient of kinetic friction

Unit 2
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 coefficient of kinetic friction μk between a wooden block and a long, horizontal wooden board. Use g = 9.8 m/s² (answers that use g = 10 m/s² are also accepted).

Part A: Available equipment

The wooden block (with a hook), the board, a set of slotted masses that can be stacked on the block, an electronic balance, a handheld force sensor, a meterstick, and a stopwatch.

Source: Hypothetical lab setup

Part B: Table 1. Another group's data (block pulled horizontally at a constant speed)

Total mass of block and added masses (kg)	Force sensor reading (N)
0.50	1.6
1.00	3.1
1.50	4.8
2.00	6.2
2.50	7.9

Source: Hypothetical data

Suggested time: 27 minutes

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Part (A(i))

3 points

Describe an experimental procedure to collect data that would allow you to determine μk. Include what you would measure and with what equipment, what you would change, and how you would make sure the force sensor reading equals the friction force.

Your answer to part (A(i))

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Part (A(ii))

2 points

Describe how you would use your data to determine μk.

Your answer to part (A(ii))

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Part (B(i))

1 point

Using the data in Table 1, indicate which quantities you would graph to produce a straight line whose slope can be used to determine μk. Calculate any values you would need.

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 μk.

Your answer to part (B(iii))

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