1- Which of the following has a largest net force? a. A 1 C charge a distance of

Question

1- Which of the following has a largest net force?

a. A 1 C charge a distance of 1 m from a -2 C charge.

b. A 1 C charge a distance of 0.5 m from a -1 C charge.

c. A 1 C charge exactly halfway between a -1 C charge and a 1 C charge separated by 2 m.

d. A 1 C charge exactly halfway between two -2 C charges separated by 2 m.

e. A 1 C charge a distance of 2m from a -4 C charge.

2- A 1C charge is placed at the origin with a 2C charge placed at the coordinates (2,0). Where should a charge of -4C be placed such that the net force on that charge is zero?

a. At x<0

b. At 0<x<1

c. At 1<x<2

d. At x>2

e. At x=0

3- Two charges of 0.5 C are placed at (0,1) and (1,0). A charge of -0.5 C is placed at (0,0).
Coordinates are in m.

Draw a force diagram on a positive charge placed at (1,1)?

What is the magnitude of the force on a 1C charge placed at (1,1)?

Explanation / Answer

1.

a) F= kq1q2/r^2 = (9*10^9*1*-2)/1^2 = -1.8*10^10 N

b) F= kq1q2/r^2 = (9*10^9*1*-1)/0.5^2 = -3.6*10^10 N

c) Fnet = F1+F2 = kq1q2/r1^2 + kq1q3/r1^2 = (9*10^9*1*1)/1^2 + (9*10^9*1*1)/1^2 = 1.8*10^10 N

d) Fnet = F1+F2 = kq1q2/r1^2 + kq1q3/r1^2 = (9*10^9*1*2)/1^2 - (9*10^9*1*2)/1^2 = 0 N

e) F= kq1q2/r^2 = (9*10^9*1*-4)/2^2 = -9.0*10^10 N

Thus b) has largest magnitude of force = -3.6*10^10 N

2.

Fnet = F1+F2 = 0

kq1q2/r1^2 + kq1q3/r1^2 =0

(9*10^9*1*2)/2^2 + (9*10^9*1*-4)/x^2 = 0

Gives x= 2.83

So charge -4C must be put to the left of 1C at a distance x= 2.83C

3.

r= sqrt(1^2+1^2) = sqrt2

F= kq1q2/r^2 = (9*10^9*1*-0.5)/(sqrt2)^2 = -2.25*10^9 N

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