Figure 3 shows how the mass of a sample of polonium-210 changes with time.
Determine the change in mass of the sample of polonium-210 between 50 and 150 days.
How to approach this question
1. Find the time of 50 days on the x-axis (horizontal axis).
2. Move vertically up from 50 days to the curve.
3. From that point on the curve, move horizontally to the left to read the mass on the y-axis (vertical axis). Note this value.
4. Repeat steps 1-3 for the time of 150 days.
5. Calculate the change in mass by subtracting the mass at 150 days from the mass at 50 days.
Full Answer
To solve this, we need to read two values from the graph and find the difference.
1. **Mass at 50 days:** Find 50 on the time axis. Go up to the line. Go across to the mass axis. The value is 420 mg. (Each small square on the y-axis is 10 mg).
2. **Mass at 150 days:** Find 150 on the time axis. Go up to the line. Go across to the mass axis. The value is 280 mg.
3. **Change in mass:** This is the difference between the two values.
Change = Mass at 50 days - Mass at 150 days
Change = 420 mg - 280 mg
Change = 140 mg
Common mistakes
✗ Misreading the scale on the axes. Each large square on the x-axis is 50 days, and on the y-axis is 100 mg.
✗ Reading only one value and not calculating the change.
✗ Simple subtraction errors.
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