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Unformatted text preview: January 20, 2009 PHY2054 Discussion-Spring ‘09 Quiz 1 (Chapter 15.1-15.9) Name: UFID: **1. (2.5pts) Two 10.0-g spheres are suspended by 25.0-cm strings as pendulums. The two pendulums are separated by 5.00 cm at the ceiling. The spheres are given the same electric charge. Find the magnitude of the charge on each sphere if each string makes 15.0º to the vertical when they are in equilibrium. The distance between two charged spheres is r = 2Lsinθ+d = 2×0.25×sin15º+0.05 = 0.179 m Since both spheres are in equilibrium, the net force on each is zero. Applying Newton’s 2 nd law to the vertical and horizontal direction, we have ΣF y = 0 Tcosθ-mg = 0 T = mg/cosθ ⇒ ⇒ ΣF x = 0 F ⇒ c-Tsinθ = 0 F ⇒ c = Tsinθ = (mg/cosθ)sinθ = mgtanθ Using Coulomb’s law we express Coulomb force in terms of charge and distance, and solve the equation for the charge. kq 2 /r 2 = mgtanθ q = √(mgtanθ/k)×r = √(0.01×9.8×tan15º/8.99×10 ⇒ 9 )×0.179 = 3.06×10-7 C **2. (2.5pts) Three point charges are located at the corners of an equilateral triangle with sides of **2....
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This note was uploaded on 12/13/2011 for the course PHY 2054 taught by Professor Avery during the Fall '08 term at University of Florida.
- Fall '08