College Physics 2e

# Chapter 18

### Problems & Exercises

1.

(a) $1.25×10101.25×1010$

(b) $3.13×10123.13×1012$

3.

-600 C

5.

$1.03 × 10 12 1.03 × 10 12$

7.

$9 . 09 × 10 − 13 9 . 09 × 10 − 13$

9.

$1.48×108C1.48×108C$

11.

(a) 0.263 N

(b) If the charges are distributed over some area, there will be a concentration of charge along the side closest to the oppositely charged object. This effect will increase the net force.

13.

The separation decreased by a factor of 5.

17.

$F = k|q1q2|r2 = ma⇒ a= kq2mr2 = (9.00×109N ⋅m2/C2) ( 1.60×10–19m)2 ( 1.67×10–27kg) ( 2.00×10–9m)2 = 3.45×1016m/s2 F = k|q1q2|r2 = ma⇒ a= kq2mr2 = (9.00×109N ⋅m2/C2) ( 1.60×10–19m)2 ( 1.67×10–27kg) ( 2.00×10–9m)2 = 3.45×1016m/s2$

18.

(a) 3.2

(b) If the distance increases by 3.2, then the force will decrease by a factor of 10 ; if the distance decreases by 3.2, then the force will increase by a factor of 10. Either way, the force changes by a factor of 10.

20.

(a) $1.04×10−91.04×10−9$ C

(b) This charge is approximately 1 nC, which is consistent with the magnitude of charge typical for static electricity

23.

$1 . 02 × 10 − 11 1 . 02 × 10 − 11$

25.
1. 0.859 m beyond negative charge on line connecting two charges
2. 0.109 m from lesser charge on line connecting two charges
28.

$8.75×10−48.75×10−4$ N

30.

(a) $6.94×10−8C6.94×10−8C$

(b) $6.25 N/C6.25 N/C$

32.

(a) $300 N/C (east)300 N/C (east)$

(b) $4.80×10−17 N (east)4.80×10−17 N (east)$

42.

(a) $2.12×105N/C2.12×105N/C$

(b) one charge of $+q+q$

44.

(a) 0.252 N to the left

(b) $x=6.07 cmx=6.07 cm$

46.

(a)The electric field at the center of the square will be straight up, since $qaqa$ and $qbqb$ are positive and $qcqc$ and $qdqd$ are negative and all have the same magnitude.

(b) $2.04×107N/C(upward)2.04×107N/C(upward)$

48.

$0.102N,0.102N,$ in the $−y−y$ direction

50.

(a) $E→=4.36×103N/C,35.0ºE→=4.36×103N/C,35.0º$, below the horizontal.

(b) No

52.

(a) $5.58×10−11 N/C5.58×10−11 N/C$

(b)the coulomb force is extraordinarily stronger than gravity

54.

(a) $−6.76×105 C−6.76×105 C$

(b) $2.63×1013m/s2(upward)2.63×1013m/s2(upward)$

(c) $2.45×10−18kg2.45×10−18kg$

56.

The charge $q2q2$ is 9 times greater than $q1q1$.

69.

(a) The forces are balanced in the x-direction, so the net force is vertical. It is composed of the sum of the vertical components of the Coulomb force and the gravitational force.

(b) No, it is in a metastable position. Since it cannot move horizontally, it cannot traverse any part of the track.

(c)

(d) Yes.

(e) It will reach $(1,− 3) (1,− 3)$ before it will change direction.

(f) The metastable positions where there is no component in one direction are $(0,0) (0,0)$, $(4,0) (4,0)$, $(2,2) (2,2)$, and $(2,−2) (2,−2)$. They number 4.

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