Physics hmwk, question

[MikeMike]

Three charges are fixed in place as shown. The squares in the grid have sides of length s = 0.24 m. The magnitude of q is 3 mu or micro Coulombs (1 mu or micro Coulomb = 10-6 Coulombs), while the magnitude of Q is 4.5 mu or micro Coulombs. What is the magnitude of the net force on q due to the other two charges?

ok, so -Q is 2s away from q and +Q is 8s away.

i got a final force of -.4028N, but it is wrong, ive tried + and -.4028 it doesnt ask for an angle or anything. but it is wrong

ive used F-k((Q1Q2) / r^2)

where Q1 would be either +Q or -Q depending upon which point charge you are calculating from, and Q2 would be q

im not sure where i went wrong, i think i might have messed up on the vectors and their numbers, but for that i got

-Q is causing a -.5267N force towards point charge -Q and +Q is causing a +.5267N force at a 135 degree angle to the -Q charge.

the +Q charge would then be split up into vectors of .3724 to the north, and to the east while the -Q has a -.5267N force to the west.

so the charges then become .1536N to the west and .3724 to the North.

which i then calculated to be the final force of .4028N to the northwest. but i cant supply any sort of direction. did i just calculate the whole final force incorrectly?

it might be confusing without a photo, but i cant supply one.

if anyone can help it would be appreciated.

http://www.ohioservers.com/pic.gif

 

[DrPizza]

Could you, perhaps, either provide a picture (as shown) or type out the units?

ok, so -Q is 2s away from q and +Q is 8s away.

How long have you been in physics? 2 seconds away??!
Or, do you mean 2 squares?

And, since you're getting the wrong answer, just what do you mean by 2 squares? Horizontally, vertically, or diagonally?

 

[MikeMike]

Originally posted by: DrPizza
Could you, perhaps, either provide a picture (as shown) or type out the units?

ok, so -Q is 2s away from q and +Q is 8s away.

How long have you been in physics? 2 seconds away??!
Or, do you mean 2 squares?

And, since you're getting the wrong answer, just what do you mean by 2 squares? Horizontally, vertically, or diagonally?

2 squares.

ill try to provide a photo. gimme a second

 

[MikeMike]

http://www.ohioservers.com/pic.gif

 

[Fenixgoon]

split the forces into components

Force Qneg = k q1q2/ 4 left

force Qpos = kq1q2 (cosine theta) / 64 right

force qpos = kq1q2 (sine theta) / 64 up

 

[MikeMike]

Originally posted by: Fenixgoon
split the forces into components

i already did that...

 

[DrPizza]

where did you get +Q is "8s away"??

 

[computeerrgghh]

HOw are +Q and q 8s away? Wouldn't it be 2root2 s away?
edit: GAH ^

 

[DrPizza]

Both Q's are 4.5 microcoulombs? (one positive and the other negative?)

And, is your problem related to the distance between q and +Q? (The distance, by pythagorean theorem is .48sqrt(2) away)

 

[MikeMike]

Originally posted by: DrPizza
where did you get +Q is "8s away"??

sh1t, i see where i fvcked up i used .48 on +q for distance instead of .6788

and i pulls that 8s from some help, i didnt type out what i actually used

 

[DrPizza]

-Q is causing a -.5267N force towards point charge -Q

Agreed.

 

[MikeMike]

Originally posted by: DrPizza
-Q is causing a -.5267N force towards point charge -Q

Agreed.

final answer was .387, i used incorrect distance to calculate the charge on q. me so stupid