19. A proton with speed  v = 3.00×105m/s orbits just outside a charged sphere. The radius of the orbit is 1.0 cm. What is the charge on the sphere? (The mass of a proton is 1.67×10−27kg.)
(A)1.04×10−9C 
(B)3.47×10−8C 
(C)6.23×10−8C 
(D)6.50×10−8C 
(E)8.28×10−7C

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統計： A(12), B(0), C(0), D(0), E(1) #2241923