P25_045 - 45. (a) The potential energy is U= q2 (8.99 109 N...

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45. (a) The potential energy is U = q 2 4 πε 0 d = (8 . 99 × 10 9 N · m 2 / C 2 )(5 . 0 × 10 6 C) 2 1 . 00 m =0 . 225 J relative to the potential energy at infnite separation. (b) Each sphere repels the other with a Force that has magnitude F = q 2 4 πε 0 d 2 = (8 . 99 × 10 9 N · m 2 / C 2 )(5 . 0 × 10 6 C) 2 (1 . 00 m) 2 =0 . 225 N . According to Newton’s second law the acceleration oF each sphere is the Force divided by the mass oF the sphere. Let m A and m B be the masses oF the spheres. The acceleration oF sphere A is a A = F m A = 0 . 225 N 5 . 0 × 10 3 kg =45 . 0m / s 2 and the acceleration oF sphere B is a B = F m B = 0 . 225 N 10 × 10 3 kg =22 . 5m / s 2 . (c) Energy is conserved. The initial potential energy is U =0 . 225 J, as calculated in part (a). The initial kinetic energy is zero since the spheres start From rest. The fnal potential energy is zero since the spheres are then Far apart. The fnal kinetic energy is 1 2 m A v 2 A +
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This note was uploaded on 11/12/2011 for the course PHYS 2001 taught by Professor Sprunger during the Fall '08 term at LSU.

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