A student measures the average speed of a bubble moving upward through a liquid at a constant speed. The stopwatch is started when the bubble is at point P. After $2.0\,\text{s}$, the bubble reaches point Q. What is the speed of the bubble from P to Q?
- A$3.2\,\text{cm s}^{-1}$
- B$3.7\,\text{cm s}^{-1}$
- C$6.4\,\text{cm s}^{-1}$
- D$7.4\,\text{cm s}^{-1}$