Physics help finding impulse by two ways

one way to find impulse is:

I = Force (average) • time

The other way is: Impulse = change in momentum (∆P) or m•v2-m•v1 (mass • vel)

so here are the values that i got:

https://docs.google.com/spreadsheet/ccc?…

For one method i get near 0.15 N•s, and for the other method i get around 1.5 N•s. I am only supposed to get like a 8% difference. I checked my units, and they seem to be alright. So there is no way for me to make the 0.15 into a 1.5 without a reason.

I'm wondering what i am doing wrong.


Just in case the link doesn't work, here is the data:

>>object one<<

Initial velocity:0.811 m/s
Final velocity: 0.668 m/s
Average Force: 1.55 N
Change in time: 1.01 s
Impulse by m•∆v: -0.149 N•s
impulse by F•∆t: 1.568 N•s


Here is my work for the first impulse method:

m•∆v = (1.0446Kg)•(0.668m/s – 0.811 m/s) = -0.149378 N•s

here is my work for the second impulse method:
= F • ∆t = 1.553 N •1.01 s = 1.56853 N•S

The initial and final velocites are in opposite directions so must have opposite signs.
When you subtract them, they actually add:

m•∆v = (1.0446Kg)•(0.668m/s – – 0.811 m/s)

m•∆v = (1.0446Kg)•(0.668m/s + 0.811 m/s) = 1.54496 N•s

(about 1.5% lower than your other answer)