Homework #1 203-1-1641 Physics 2 for Students of Structural Engineering
Part A
8. In Fig. 25-20, find (a) the horizontal components and (b) the vertical components of the resultant electric force on the charge in the lower left corner of the square. Assume that q =
1.13 x 10
-6
C and a = 15.2 cm. The charges are at rest.
16. Find the force on a positive point charge q located a distance x from the end of a rod of length L with uniformly distributed positive charge Q . (See Fig. 25-21)
24. The electrostatic force between two identical ions that are separated by a distance of 5.0 x
10
-10 m is 3.7 x 10
-9
N. (a) Find the charge on each ion. (b) How many electrons are missing from each ion?
Part B
1. Two identical conducting spheres, having charges of opposite sign, attract each other with a force of 0.108 N when separated by 50.0 cm. The spheres are suddenly connected by a thin conducting wire, which is then removed, and thereafter the spheres repel each other with a force of 0.0360 N. What were the initial charges on the spheres?

4. Two similar tiny balls of mass m are hung from silk threads of length L and carry equal charges q as indicated in Fig. 25-22. Assume that

is sufficiently small so that tan
 
sin

. (a) In this approximation show that, for equilibrium, x = [( q
2
L )/(2
 o mg )]
1/3
, where x is the separation between the balls. (b) If L = 122 cm, m = 11.2 g, and x = 4.70 cm, what is the value of q ?
6. Assume that each ball in question 4 (Fig. 25-22) is losing charge at the rate of 1.2 nC/s. At what instantaneous relative speed (= dx / dt ) do the balls approach each other initially?
10. In the compound CsCI (cesium chloride), the Cs atoms are situated at the corners of'a cube with a Cl atom at the cube's center. The edge length of the cube is 0040 nm; see Fig.
25-23. The Cs atoms are each deficient in one electron and the Cl atom carries one excess electron. (a) What is the strength of the net electric force on the Cl atom resulting from the eight Cs atoms shown? (b) Suppose that the Cs atom marked with an arrow is missing
(crystal defect). What now is the net electric force on the Cl atom resulting from the seven remaining Cs atoms?