Answer: a) 1.6 * 10 ^-7 N/C (upward) ; b) -2.5*10^-6N (downward)
Explanation: In order to solve this proble we have to use the Coulomb law given by:
F=q*E from this expression we have
E=F/q=4.8*10^-6/30 C= 1.6 * 10 ^-7 N/C
The force on the particle charge by -1.6 X10 C place intead of the initial charge we have
F=q*E= -16 C* 1.6 * 10 ^-7 N/C= -2.5*10^-6N