In an experiment designed to find the acceleration of free fall $g$, a ball-bearing is supported by an electromagnet. Once the current to the electromagnet is turned off, a clock begins and the ball-bearing drops. After travelling a distance $h$, the ball-bearing hits a switch that stops the clock, which records the time $t$ for the fall. Which expression can be used to calculate the value of $g$?
- A$\frac{h t^2}{2}$
- B$\frac{t h^2}{2}$
- C$\sqrt{\frac{2t}{h^2}}$
- D$\frac{2h}{t^2}$