Exercise 23.5 Constants Part A A small metal sphere, carrying a net charge of g-

Question

Exercise 23.5 Constants Part A A small metal sphere, carrying a net charge of g-260 AC, is held in a stationary position by insulating supports. A second small metal sphere, with a net charge of Q2 =-8.00 C and mass 1 40 g , is projected toward gh. When the two spheres are 0.800 m apart, q is moving toward g, with speed 22.0 m/s (Figure 1) Assume that the two spheres can be treated as point charges. You can ignore the force of gravity What is the speed of when the spheres are 0 390 m apart? v 11.5 m/s Previous Answers Correct Part B How close does qa get to Figure 1 of 1 Im Submit xIncorrect, Try Again: 2 attempts remaining Y2 u=22.0 m/s 9i Provide Feedback 0.800 m

Explanation / Answer

At the minimum distance between, q1 and q2, speed of q2 =0. Hence at that position, all the Kinetic energy of q2, is used to increase potential energy of charges.
Initial potetial energy of charges = k q1 q2 /0.8
At minimum distance, r potential energy = kq1 q2 / r
increase in potential energy = k q1 q2 (1/r - 1/0.8) .....1
Kinetic energy of q2 when at distance 0.8 m = mv2/2 = 1.4x10-3 * 222/2   ....2

equating 1 and 2 we get
k q1 q2 (1/r - 1/0.8) = 1.4x10-3 * 222/2
9x109 * (8*2.6x 10-12) (1/r - 1/0.8) = 1.4x10-3 * 222/2
r = 0.327 m

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