physics circular motion flash cards

6. A -2.3×10^-6C charge exerts a repulsive force of magnitude 0.35N on an unknown charge 0.20m away. What are the magnitude and polarity of the unknown charge?

F=KQq/r²

q=(0.35)(0.2)²/(9.0×10^9)(-2.3×10^-6)

=-6.8×10^-7

7. Two point charges 2.5×10^-6C and -5×10^-4C are placed 3.0m apart. What is the magnitude of the electric field at point P, midway between two charges

E1=KQq/r²

(9×10^9)(2.5×10^-6)/(1.5)²

=1.0×10^4

E2=(9×10^9)(-5×10^-4)/(1.5)²

=2.0×10^4

ET=E1+E2

=3.0×10^4N/C

8. A 4.0×10^-9C change is initially located 3.0m from a stationary 6.0×10^-8C charge. How much work is required to move the 4.0×10^-9C charge to a point 0.50m from the stationary charge?

W=PE

=q(Vf-Vi)

4.0×10^-9C ((9.0×10^9)(6×10^-8)/0.5)-((9.0×10^-9)(6×10^-8)/3)0

=3.6×10^-6J

9. Two parallel plates 4.0×10^-2m apart have a potential difference of 1000V. An electron is released from a negative plate at the same instant that a proton is released from the positive plate. What compares their speed and kinetic energy as they strike the opposite plate?

Speed of Electron and Proton: different

Kinetic Energy of Electron and Proton: same

10. Two positive charges, equal in magnitude, are separated. In which location would the electric field strength be zero?

2