Charge Q = 70 mu C is distributed uniformly over the volume of an insulating sph
ID: 1630288 • Letter: C
Question
Charge Q = 70 mu C is distributed uniformly over the volume of an insulating sphere that has radius R = 10.0 cm. A small sphere with charge q = +2.00 mu C and mass 6.00 times 10^-5 kg is projected toward the center of the large sphere from an initial large distance. The large sphere is held at a fixed position and the small sphere can be treated as a point charge. What minimum speed must the small sphere have in order to come within 8.00 cm of the surface of the large sphere? Express your answer with the appropriate units. v = ____________Explanation / Answer
initially
eletric PE, PEi = 0
Kinetic energy, KEi = m v^2 /2
When r = 8 cm = 0.08 m
PEf = k q1 q2 / r = (9 x 10^9) (7 x 10^-6)(2 x 10^-6)/ 0.08
= 1.575 J
KEf = 0 (finally it stops)
Applying energy conservation,
PEi + KEi = PEf + KEf
0 + m v^2 /2 = 1.575 + 0
v = 229.2 m/s