Question

How do I calculate my reaction time using appropriate uniform acceleration equation?

Answer 1

I had to determine my human reaction time (the time it takes for me to react to an event, which in this case is catching a 30 cm ruler).

Answer 2

I did it three times and I got 8 cm, 12.5 cm, and 9.5 cm, which if I average = 10 cm.

Answer 3

How do I calculate my reaction time using the appropriate uniform acceleration equation?

Answer 4

So think about what factors you know and don't know. Acceleration due to gravity is 9.8 m/s^2, the initial velocity of the ruler was 0, the initial location of the ruler was 0, and you know the final location of the ruler is 10 cm. Using this information you can find time with the formula

Xfinal = Xinitial + Velocityinitial*time+1/2*acceleration*time^2

Answer 5

If you have trouble factoring out the time, use the quadratic formula and since you can not have a negative reaction time, you know which of the two answers is correct.

Answer 6

yes, that I know.
Ohh...

Answer 7

what is x initial?

Answer 8

The initial location of the ruler is X initial while X final is the distance it fell in centimeters. Don't forget the acceleration I gave you above was in meters, so you'll want to convert it to 980 centimeters/second^2

Answer 9

can I do it with d/v = time?

Answer 10

No, because there is no constant velocity. Velocity increases over time at a rate of 9.8 m/s^2.

Answer 11

ohhh, okay.

Answer 12

Is there another word for xfinal? Like a symbol?

Answer 13

None that comes to mind, but I'm sure there are textbooks out there that use different variable names. It doesn't really matter what we call them, you could call it Y or Q or Purple Square, but as long as it's the initial location (distance at time = 0) that's really all that matters. Since the ruler was dropped from the 0cm mark, that is where we first let go while 10cm later when you caught it, that's when the ruler was speeding up and going faster and faster, although not by a lot in the time it took for you to catch it. I hope that helps.

Answer 14

because I've never heard of xfinal or xinitial before...

Answer 15

ohhh.. okay.

Answer 16

thank you :)

Answer 17

it's just that

Answer 18

Yeah, in this formula Xinitial would be = 0, and normally it is 0, so usually when people learn formulas, the variable isn't there since adding 0 doesn't really change anything at all. =D

Answer 19

on my textbook there are 5 equations i can use for this problem:

-> -> ->
Aav = Vf - Vi
--------
delta t

Answer 20

delta -> -> ->
d = Vi delta t + Aav(delta t)^2
------------
2

Answer 21

Velocity final = Velocity initial + Acceleration*time is the same formula

however you don't know the final velocity to use that formula to solve for change in time (delta t)

The other equation you know is Xfinal = Xinitial +()Velocity final +Velocity initial)/2)*time

Answer 22

ohh, i see.

Answer 23

So what you do is do substitution and plug in like this... I'll draw it out.