HW2 - johnson (rj6247) hw 2 Opyrchal (121014) 1 This...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: johnson (rj6247) hw 2 Opyrchal (121014) 1 This print-out should have 14 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points Three point charges, two positive and one negative, each having a magnitude of 38 C are placed at the vertices of an equilateral triangle (38 cm on a side). a-q +q +q The Coulomb constant is 8 . 98755 10 9 N m 2 / C 2 . What is the magnitude F of the electro- static force on one of the positive charges? Correct answer: 89 . 8755 N. Explanation: Let : q = 38 C , a = 38 cm , and k e = 8 . 98755 10 9 N m 2 / C 2 . The magnitude of electrostatic force is F = k e | q 1 | | q 2 | r 2 The answer is independent of the exact orien- tation of the triangle, but lets choose a par- ticular orientation ( i.e. , choose a coordinate system) to use for our calculations. Consider the arrangement of charges where the nega- tive point charge is positioned at the origin and one of the positive charges is located at x = a . Then consider the electrostatic force on the upper positive charge, which we call A ; ( i.e. , A be in the first quadrant). First, note that by symmetry and by the fact that neg- ative charge exerts an attractive force while the positive charge exerts a repulsive force, F y = 0 . This leaves us with only the x component of the force on A . Using the principle of super- position, and recalling that for an equilateral triangle, = 60 : F = 2 parenleftbigg k e q 2 a 2 parenrightbigg cos 60 = k q 2 a 2 since cos 60 = 1 2 , so F = k e q 2 a 2 = ( 8 . 98755 10 9 N m 2 / C 2 ) ( 3 . 8 10 5 C ) 2 (0 . 38 m) 2 = 89 . 8755 N . 002 (part 1 of 2) 10.0 points Two charges are located on a horizontal axis. The Coulomb constant is 8 . 98755 10 9 N m 2 / C 2 . 1 . 4 C 1 . 4 C p 1 . 6 m 3 m 3 m Determine the electric field at p on a verti- cal axis as shown in the figure above. Up is the positive direction. Correct answer: 1024 . 43 V / m. Explanation: Let : x = 3 m , y = 1 . 6 m , q = 1 . 4 C , and k e = 8 . 98755 10 9 N m 2 / C 2 . E E q q y x- x johnson (rj6247) hw 2 Opyrchal (121014) 2 The distance from each point charge to the point of interest on the y-axis is r = radicalbig x 2 + y 2 = radicalBig (3 m) 2 + (1 . 6 m) 2 = 3 . 4 m . Therefore, the electric field due to one of the point charges is E = k e q r 2 = (8 . 98755 10 9 N m 2 / C 2 )(1 . 4 10 6 C) (3 . 4 m) 2 = 1088 . 46 V / m ....
View Full Document

Page1 / 6

HW2 - johnson (rj6247) hw 2 Opyrchal (121014) 1 This...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online