Measuring Human Reaction Time with a Ruler

[Dgolverk]

Hello,
I need some help figuring out how to proceed.

Homework Statement

Make up a ruler, that can measure human reaction time in time intervals of 0.05s. There supposed to be 6 intervals in total.
We did a similar experiment in class, where a student drops a ruler and I need to catch it as fast as I can. The displacement (cm as shown on the ruler) was 17cm.

The Attempt at a Solution

I used a uniform acceleration equation: displacement = (Initial Velocity)(change in time) + 1/2(Acceleration due gravity)(change in time)^2
and found the time to be 0.18s for the 17 cm.

So now I need to make a ruler that will calculate time instead of displacement.
However I don't know what values to use every 0.05s on the ruler.

 

[member 553083]

I know the final time is 0.18s but I don't know what the initial time is to start off the ruler. Can anyone help me out? Thanks a lot! The equation you used is fine for finding the time taken for the object to fall 17 cm. However, to make your ruler, you will need to find the displacement (or distance) at regular intervals of 0.05s. To do this, you could use the same equation with changing times. Let's start with the first interval, from 0 s to 0.05s. The initial velocity is 0, and the acceleration due to gravity is -9.8 m/s2. Therefore, the displacement in this interval would be 0.5 x (-9.8)(0.05)^2 = -0.00245m, or 2.45 mm. You can then repeat this process for each interval and fill in the displacements on your ruler. For example, for the second interval, from 0.05s to 0.1s, the displacement would be 0.5 x (-9.8)(0.1)^2 = -0.00980m, or 9.8 mm. Once you have the displacements for each interval, you can convert them into time values by solving the equation you used earlier (displacement = (Initial Velocity)(change in time) + 1/2(Acceleration due gravity)(change in time)^2). This should give you the time taken for each interval, which you can then use to make up your ruler.