- #1
roam
- 1,271
- 12
Homework Statement
Three small spheres are placed at fixed points along the x-axis, whose positive direction points towards the right.
Sphere A is at x = 46.0 cm, with a charge of –6.00 μC.
Sphere B is at x = 55.0 cm, with a charge of 6.00 μC.
Sphere C is at x = 59.0 cm, with a charge of –7.00 μC.
(a) Calculate the magnitude of the electrostatic force on sphere B.
(b) What would be the magnitude of the electric field at the point where sphere B was located?
Homework Equations
Coulomb's law [tex]\vec{F_{1,2}}= k_e \frac{q_1q_2}{r^2}[/tex]
electric field: [tex]\vec{E}=\frac{\vec{F_e}}{q_0}[/tex]
[tex]\vec{E}= k_e \frac{q}{r^2}[/tex]
The Attempt at a Solution
For part (a), I have used Coulomb's law as follows:
[tex]\vec{F_{A,B}}= (8.9 \times 10^9) \frac{(6 \times 10^{-6} C) (6 \times 10^{-6} C)}{9^2}[/tex]
= 3.95 x 10-3 N
[tex]\vec{F_{C,B}}= (8.9 \times 10^9) \frac{(7 \times 10^{-6} C) (6 \times 10^{-6} C)}{4^2}[/tex]
= 0.02336 N
Taking FA,B as negative and FC,B to be positive:
0.02336 - 3.95 x 10-3 N = 0.0194 N
But the answer must be 196 N. What's wrong?
(b) I tried the 3rd equation equation above but it didn't work...
[tex](8.9 \times 10^9) \frac{196}{9^2} = 2.15 \times 10^{10}[/tex]
Again this is wrong. It must be 32700000 N/C. Any help with this problem is appreciated.