A test charge of -5.0 x 10-7 C is placed between other charges so that it is 50 mm from a charge of -3.0 x 10-7 C and 10 cm from a charge of -6.0 x 10-7 C. The three charges lie along a straight line.
A) What is the magnitude and direction of the force on the test charge?
B) Where would the test charge have to be located in order to be in equilibrium?

I tried it but I can't get the answer for b

Question

A test charge of -5.0 x 10-7 C is placed between other charges so that it is 50 mm from a charge of -3.0 x 10-7 C and 10 cm from a charge of -6.0 x 10-7 C.   The three charges lie along a straight line.  
A)  What is the magnitude and direction of the force on the test charge?
B)  Where would the test charge have to be located in order to be in equilibrium?


I tried it but I can't get the answer for b

anonymous · Answer

|dw:1367547447194:dw|
this is the diagram for part b
solve for "x" 
such that the two forces are equal

anonymous · Answer

why is there 60-x, were did it come from

anonymous · Answer

Q1and Q2 are separated by a distance of 60mm

anonymous · Answer

|dw:1367547820534:dw|

anonymous · Answer

if Qt is at a distance of "x" from Q1, it will be at a distance of "60-x" from Q2.