AP Physics C E and M

Question

Three point charges are located along the x-axis: q₁ = +5.0 μC is at 20 cm, q₂ = +4.0 μC is at 0 cm, and q₃ = +10.0 μC is at –30 cm. What is the net electrostatic force on q₂?

0.50 N to the left

500 N to the right

0.50 N to the right

8.5 N to the left

Answer 1

Calculate magnitudes of electric forces and work out in what direction they operate. Then add the forces vectorially.

|F_1on2| = k_eQ₁Q₂/d₁₂² to the left and |F_3on2| = k_eQ₂Q₃/d₃₂² to the right

k_e = 8.99 x 10⁹ in MKS. μC are 10^-6C and the distances need to be in meters.

F_net = F₁₂-F₃₂ with a negative value indicating to the left.