A resistor R and a capacitor C are connected in series to a battery of terminal voltage V0. Which of the following equations relating the current I in the circuit and the charge Q on the capacitor describes this circuit? (A) V0 + QC – I2R = 0
(B) V0 – Q/C – IR = 0
(C) V02 – Q2/2C – I2R = 0
(D) V0 – CI – I2R = 0
(E) Q/C – IR = 0

Aspring with an unstrained length of 0.071 m and a spring constant of 2.6 n/m hangs vertically downward from the ceiling. a uniform electric field directed vertically upward fills the region containing the spring. a sphere with a mass of 5.29 10-3 kg and a net charge of +7.2 µc is attached to the lower end of the spring. the spring is released slowly, until it reaches equilibrium. the equilibrium length of the spring is 0.058 m. what is the magnitude of the external electric field?