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 that air has no effect on the ruler?
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 falls due to gravity, so we use the formula: 
d = 1/2*g*t^2 
where d is the distance fallen, g is the acceleration due to gravity (9.8 m/s^2), and t is the reaction time (assumed to be 0.10 s). 
Plugging in the values, we get: 
d = 1/2 * 9.8 m/s^2 * (0.10 s)^2 
d = 0.049 m = 4.9 cm 
Therefore, the ruler will fall at least 4.9 cm before it is caught.

Human Reaction Time Is Usually Greater Than 0