The diagram illustrates an experiment for measuring the speed of a small ball as it falls through a clear liquid inside a glass tube at constant speed. Two marks are drawn on the tube. The upper mark is at $115 \pm 1\,\text{mm}$ on the nearby rule, while the lower mark is at $385 \pm 1\,\text{mm}$. The ball crosses the upper mark at $1.50 \pm 0.02\,\text{s}$ and crosses the lower mark at $3.50 \pm 0.02\,\text{s}$. The constant speed of the ball is found using $\dfrac{385 - 115}{3.50 - 1.50} = \dfrac{270}{2.00} = 135\,\text{mm s}^{-1}$. Which expression is used to calculate the fractional uncertainty in this speed value?
- A$\dfrac{2}{270} + \dfrac{0.04}{2.00}$
- B$\dfrac{2}{270} - \dfrac{0.04}{2.00}$
- C$\dfrac{1}{270} \times \dfrac{0.02}{2.00}$
- D$\dfrac{1}{270} \div \dfrac{0.02}{2.00}$