Human reaction time is usually greater than 0.10 s. If your friend holds a ruler between your fingers and releases it without warning, how far can you expect the ruler to fall before you catch it, assuming negligible air resistance?
A) At least 3.0 cm
B) At least 4.9 cm
C) At least 6.8 cm
D) At least 9.8 cm

Question

Quizplus · Accepted Answer

Assuming negligible air resistance, the ruler will fall freely with an acceleration of g = 9.8 m/s². During the time it takes for a person to react and catch the ruler, the ruler will have fallen the distance d given by:
d = 1/2 * g * t²
Where t is the reaction time. Given that human reaction time is usually greater than 0.10 s, we have:
t = 0.10 s
So, d = 1/2 * 9.8 m/s² * (0.10 s)² = 0.049 m = 4.9 cm. Therefore, the answer is B.

Human Reaction Time Is Usually Greater Than 0