Solving for Charge Q at Corner C in Electric Field Problem

AI Thread Summary
In the electric field problem involving square ABCD, a positive charge Q is placed at corner A, and the goal is to determine the charge q needed at corner C to ensure the net electric force on A is zero. The forces acting on A include repelling forces from charges at corners B and D, which are both positive, necessitating that charge q at C be negative to neutralize these forces. Calculations initially suggested a required force of 7.9N to balance the forces on A, leading to an estimated charge of q at 3.51 * 10^-8. However, feedback indicated that this value was significantly underestimated by a factor of 1000, and adjustments were needed to account for the diagonal distance in the force calculations. The discussion reflects a collaborative effort to verify and correct the calculations involved in solving for charge q.
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Homework Statement



In the square ABCD every corner is marked (from the left top corner, moving to the right) D, C, B, A, we have places a positive charge Q = 2,5 * 10-8. In the corner C a charge of q should be placed so the total of electricforces on A = 0. The distans between A and D is 1,0mm. Should the charge q places on corner C be positiv or negative and decide what charge of q that needs to be placed at corner C

Homework Equations



F= k*Q1*Q2/r2

The Attempt at a Solution



What i started to do was to write down the forces affecting the charge A. Which was a repelling force from B facing to the left at charge A and a repelling force from D facing down at charge A. What we now know is that charge C has to somehow "neutralize" these forces, thus the charge C has to be negative.

After have written down the forces affecting A we can se the that the total force affecting A is a diagonal facing "South west". By using F= k*Q1*Q2/r2 we can decide the repelling forces affecting A (i got 5,6N) and then use these forces by the help of pythagoras theorem to decide the diagonal (i got 7,9N). We now know the total force and thus an attracting force of 7,9N should neutralize the forces and the total outcome should result into A=0. Using F= k*Q1*Q2/r2 again although leaving one charge Q unknown and substituting F with 7,9N i got the the charge Q has to be 3,51*10-8

I really hope this made sense for you guys, when i started with the quest i actually had no idea to do it so now I'm just curios to see if i have the right solution :P

Thanks for taking a look! =)
 
Last edited:
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Your answer for the net force of B and D is correct. Your answer for Q is much too small. I think it's a factor 1000 too small, and on top of that I think you didn't use that the diagonal is longer, so will be bigger in the equation for the force between A and C
 
Yeah sorry i just noticed my mistake it should be correct now i edited everything, does it seem correct now?

Thanks for answering
 
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
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