Giancoli 5th Ed.

Ch. 21 P. 1-3,7,8,10,12,13
       Q. 1-14 (don't write out)
       MiscQ. 1-3

Problems
1. F = k q1*q2/r^2  = 2.7e-3 N
2. Q/e = 3.62e+14 electrons
3. F = k q1*q2/r^2  = 1.2e+4 N
7. F/F' = (r'/r)^2,  so r = 3.59 cm
8. n_e = Q/e = 2.1e+14 electrons
   m_electrons = 1.9e-16 kg
10. F_E/F_G = 2.27e+39
12. Left charge: F_+82 = -150 N i   (to the left)
    Middle charge: F_+48 = 620 N i  (to the right)
    Right charge: F_-95 = -480 N i (to the left)
13. Use F_tot = vector sum of all forces (superposition principle)
    Top charge feels: F_top = 200 N j (up)
                 or:  F_top = 200 N away from center of triangle
    Bot right charge: F_BR = 173.4 i - 100.1 j  N  
                 or:  F_BR = 200 N away from center of triangle
    Bot left charge: F_BL = -173.4 i - 100.1 j  N
                 or:         200 N away from center of triangle

Misconceptual Questions
1. a
The two charges have opposite signs, so the force is attractive. Since 2 Q is 
located on the positive x-axis relative to 1 Q at the origin, the force on 1 Q 
will be in the positive x-direction.

2. d
The signs of the charges are still opposite, so the force remains attractive. 
However, since 2 Q is now located at the origin with 1 Q on the positive x-axis, 
the force on 1 Q will now be toward the origin, or in the negative x-direction.

3. e
A common misconception is that the object with the greater charge and smaller mass 
has a greater force of attraction. However, Newton’s third law applies here. 
The force of attraction is the same for both lightning bugs.