Q: Three charges are located on the x-axis: $$q_1 = +2$$\ \mu C$$ at x = 0$, q_2$ = -3\ \mu C at$$ $$x = 1 m$$, and $$q_3 = +4$$\ \mu C$$ at x = 2$ m. What is the net force on q_2$?

$$F = 0.108 N$\ (\text{to the right})$$

Q: Which constant is used in Coulomb's Law and what is its value?

$$k = 9 \times 10^9$ N$$\cdot$$m^2$/C^2$

Question 1

Which of the following correctly expresses Newton's Law of Universal Gravitation?

Accepted Answer

$$F = G \frac{m_1$ m_2$}{r^2$}$$

Question 2

Coulomb's Law describes the force between two point charges. Which of the following is the correct formula?

Accepted Answer

$$F = \frac{1}{4\pi\$$epsilon_0$$} \frac{q_1$ q_2$}{r^2$}$$

Question 3

Which of the following statements about gravitational force is correct?

Accepted Answer

It is always attractive.

Question 4

If the distance between two charges is tripled, what happens to the electrostatic force between them?

Accepted Answer

It decreases by a factor of 9.

Question 5

Two charges, $$q_1$$ and $$q_2$$, are separated by a distance $$r. If$$ $$q_1 is $$doubled and $$r is $$halved, how does the force change?

Accepted Answer

It becomes 8 times larger.

Question 6

Which of the following best describes the difference between gravitational and electrostatic forces?

Accepted Answer

Electrostatic force can be attractive or repulsive; gravitational force is always attractive.

Question 7

Consider a hydrogen atom with an electron and a proton separated by $$r = 5.3 	imes 10$$^{-11}$$ m. Which force is stronger between them?

Accepted Answer

The electrostatic force is stronger.

Question 8

If two balls with charges $$+Q$$ and $$-Q$$ are separated by a distance $$3d$$, where should a third charge be placed so that the net force on it is zero?

Accepted Answer

At a distance $$2d$$ from $$+Q.$$

Question 9

A proton and an electron are held apart at a distance $$d. $$Which particle experiences a larger acceleration due to the force between them?

Accepted Answer

The electron, because it is lighter.

Question 10

Three charges are located on the x-axis: $$q_1 = +2$$\ \mu C$$ at x = 0$, q_2$ = -3\ \mu C at$$ $$x = 1 m$$, and $$q_3 = +4$$\ \mu C$$ at x = 2$ m. What is the net force on q_2$?

Accepted Answer

$$F = 0.108 N$\ (	ext{to the right})$$

Question 11

Two 2.5 g pith balls hang at the ends of 60 cm strings and are equally charged so that each makes an angle of $$10^\circ$$ with the vertical. What is the magnitude of the charge on each ball?

Accepted Answer

$$q = 1.2 	imes 10$$^{-7}$$ C

Question 12

Which of the following best represents the direction of the net force on a positive charge due to a $$-3Q$$ charge to the left and a $$+4Q$$ charge to the right?

Accepted Answer

To the right

Question 13

If the force between two charges is $$F$$ and the distance between them is doubled, what is the new force?

Accepted Answer

$$F/4$$

Question 14

Which constant is used in Coulomb's Law and what is its value?

Accepted Answer

$$k = 9 	imes 10^9$ N$$\cdot$$m^2$/C^2$

Question 15

Which of the following is a correct statement about the electrostatic force?

Accepted Answer

It can be either attractive or repulsive.

Coulomb’s Law and the Electrostatic Force: Concepts, Comparisons, and Applications

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