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

The ruler will fall for the amount of time it takes for your brain to process the information and send a signal to your hand to catch it. This time is at least 0.10 s. Using the equation d = 1/2gt^2, where g is the acceleration due to gravity (9.8 m/s^2) and t is the time the ruler falls before being caught, we can calculate the minimum distance the ruler will fall before being caught. 
d = 1/2gt^2 
d = 1/2 * 9.8 m/s^2 * (0.10 s)^2 
d = 0.049 m 
d = 4.9 cm 
Therefore, we can expect the ruler to fall at least 4.9 cm before being caught.

Human Reaction Time Is Usually Greater Than 0