(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

If you had a simple pendulum of length 1 m and mass 5e-3 kg placed in a uniform electric field E that is directed vertically upward. The bob has charge of -8e-6 C. the period is 1.2 s what are the magnitude and direction of E?

First, didn't they already tell us that E is directed vertically upward, so wouldn't the direction of E be vertically upward? Though wouldn't there be a force downward on the charge from E if that is the case?

Also, I thought that the period for the simple pendulum is sqrt(L/g), where L is the length measured from the pivot and g is gravity. So here sqrt(L/g) doesn't come out to be 1.2 s?

Would the force from the Field qE = the torque that causes it to oscillatte (but can we ignore gravity?) And since F = ma, so we know that qE/m = a. And we also know that the angular acceleration on a pendulum is Lmgsin(theta)/I, where I is the moment of inertia of the pendulum. So does this mean that the two are equal (after I multiply the angular acceleration by L)? But then what about theta?

Thanks.

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Electric Field Problem and simple pendulum

**Physics Forums | Science Articles, Homework Help, Discussion**