### Sample Problem Dropping a stone into a well that is 7 m deep creates a sound. How much time elapses before you hear the splash? **Strategy** Total time is the time for the stone to drop plus the time for the sound wave to travel up the well. **Translation** Read the problem and create math statements to match the English. Assign a symbol to each physical quantity. Remember to include the standard (SI Unit as the multiplier for the magnitude of the physical quantity). **Given** There are three physical quantities given or known to us. There are three unknown quantities (times) $s = 7 m$ $g = 9.81 m/s$ $v = 343 m/s$ **Unknown** $t_1 = ?? s$ $t_2 = ?? s$ $t = ?? s$ This information leads us to three equations. **Time to Drop** ($t_1$) $s = \frac{1}{2}g \ {t_1}^2 \tag{1}$ $t_1 = \sqrt{\frac{2s}{g}}$ **Time for sound to travel** ($t_2$) $v = \frac{s}{t_2}$ $t_2 = \frac{s}{v}$ **Total Time** $t = t_1 + t_2$