# Forces in action help

#### EdZ

Hey ppls, how r ya? i have a few questions ...

http://www.boomspeed.com/asianedz/Untitled.jpg [Broken]

yeh i have the resolution to it although it is my friends one. i dun really understand how he got it... can some1 plz explain to me clearly how he did it and if the answer is right?

here are the resolution...

http://www.boomspeed.com/asianedz/Untitled2.jpg [Broken]

http://www.boomspeed.com/asianedz/Untitledm.jpg [Broken]

EdZ

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#### ottjes

first show where you got stuck (policy)
then we'll be glad to help

#### EdZ

actually forget that one, i read it a few times over again and i understood how to do it.

but i do have one question, i was wondering

what is the procedure to find the error on an equation..

for e.g.

4.7 +- 0.5 * 45.64 +- 0.21 / 32.233 +- 0.923

what are the steps in identifying where the error is.?

#### enigma

Staff Emeritus
Gold Member
The easiest way I've found is to keep the units on your numbers. (I must sound like a broken record... I've said this three times since we switched to the new forums alone)

If you are adding, all summed units must be the same.

All units must also be the same on both side of the equality sign.

#### EdZ

sorry, i dont quite understand what your saying... can u please explain again...

sorry, :(

#### enigma

Staff Emeritus
Gold Member
For example,

In your friend's solution for the first problem.

Instead of writing 20-3a=2a

write 20 N - 3kg*a = 2kg*a

You know then, that every term is the same.

It's not a big thing for a simple problem like this, but once you get more things in there, it's an easy way to check yourself.

If the units don't add up on both sides of the equal sign, you've made a mistake.

#### EdZ

ahh ok ok... im with u now... i thought u were talking about my other question which was to do with error analysis...

yes i will keep that in mind.. thankyou!

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