### Measuring Reaction Time

Use the formula (b) The time to fall is $y=-gt^{2}/2,$ but only keep the absolute value. Then:
$y_{50} = \frac{1}{2}(9.8\frac{m}{s^{2}})(0.05s)^{2}=1.2cm$
$y_{100} = \frac{1}{2}(9.8\frac{m}{s^{2}})(0.10s)^{2}=4.9cm$
$y_{150} = \frac{1}{2}(9.8\frac{m}{s^{2}})(0.15s)^{2}=11cm$
$y_{200} = \frac{1}{2}(9.8\frac{m}{s^{2}})(0.20s)^{2}=20cm$
$y_{250} = \frac{1}{2}(9.8\frac{m}{s^{2}})(0.25s)^{2}=31cm.$