Deck 23: Electric Forces

Question 1

A particle (m = 50 g, q = 5.0 μC) is released from rest when it is 50 cm from a second particle (Q = −20 μC). Determine the magnitude of the initial acceleration of the 50-g particle.

A)54 m/s²
B)90 m/s²
C)72 m/s²
D)65 m/s²
E)36 m/s²

Answer 1

72 m/s²

Question 2

Identical point charges Q are placed at each of the four corners of a 3.0-m × 4.0-m rectangle. If Q = 40 μC, what is the magnitude of the electrostatic force on any one of the charges?

A)3.0 N
B)2.4 N
C)1.8 N
D)3.7 N
E)2.0 N

Answer 2

2.4 N

Question 3

A particle (charge = +40 μC) is located on the x axis at the point x = −20 cm, and a second particle (charge = −50 μC) is placed on the x axis at x = +30 cm. What is the magnitude of the total electrostatic force on a third particle (charge = −4.0 μC) placed at the origin (x = 0)?

A)41 N
B)16 N
C)56 N
D)35 N
E)72 N

Answer 3

56 N

Question 4

Three point charges are positioned on the x axis. If the charges and corresponding positions are +32 μC at x = 0, +20 μC at x = 40 cm, and −60 μC at x = 60 cm, what is the magnitude of the electrostatic force on the +32-μC charge?

A)84 N
B)12 N
C)36 N
D)50 N
E)48 N

Question 5

If a = 3.0 mm, b = 4.0 mm, Q1 = 60 nC, Q2 = 80 nC, and q = 32 nC in the figure, what is the magnitude of the electric force on q?

A)1.6 N
B)1.3 N
C)1.9 N
D)2.2 N
E)0.040 N

Question 6

A point charge Q is placed on the x axis at x = −2.0 m. A second point charge, −Q, is placed at x = 1.0 m. If Q = 60 μC, what is the magnitude of the electrostatic force on a 40-μC charge placed at the origin?

A)16 N
B)27 N
C)32 N
D)11 N
E)3.0 N

Question 7

Three identical point charges Q are placed at the vertices of an equilateral triangle (length of each side = 2.0 m). If Q = 60 μC, what is the magnitude of the electrostatic force on any one of the charges?

A)25 N
B)19 N
C)14 N
D)22 N
E)16 N

Question 8

In the figure, if Q = 30 μC, q = 5.0 μC, and d = 30 cm, what is the magnitude of the electrostatic force on q?

A)15 N
B)23 N
C)zero
D)7.5 N
E)38 N

Question 9

A charge of +80 μC is placed on the x axis at x = 0. A second charge of −50 μC is placed on the x axis at x = 50 cm. What is the magnitude of the electrostatic force on a third charge of 4.0 μC placed on the x axis at x = 30 cm?

A)13 N
B)77 N
C)39 N
D)25 N
E)45 N

Question 10

If Q = 25 μC, q = 10 μC, and L = 40 cm in the figure, what is the magnitude of the electrostatic force on q?

A)28 N
B)22 N
C)20 N
D)14 N
E)10 N

Question 11

A point charge Q is placed on the x axis at the origin. An identical point charge is placed on the x axis at x = −1.0 m and another at x = +1.0 m. If Q = 40 μC, what is the magnitude of the electrostatic force on the charge at x = +1.0 m?

A)29 N
B)14 N
C)11 N
D)18 N
E)7.0 N

Question 12

If a = 3.0 mm, b = 4.0 mm, Q1 = −60 nC, Q2 = 80 nC, and q = 30 nC in the figure, what is the magnitude of the electric force on q?

A)1.4 N
B)1.0 N
C)1.7 N
D)2.0 N
E)0.50 N

Question 13

A point charge (−5.0 μC) is placed on the x axis at x = 4.0 cm, and a second charge (+5.0 μC) is placed on the x axis at x = −4.0 cm. What is the magnitude of the electric force on a third charge (+2.5 μC) placed on the y axis at y = 3.0 cm?

A)90 N
B)45 N
C)54 N
D)72 N
E)36 N

Question 14

If Q = 20 μC and L = 60 cm, what is the magnitude of the electrostatic force on any one of the charges shown?

A)25 N
B)19 N
C)15 N
D)9.1 N
E)14 N

Question 15

If a = 3.0 mm, b = 4.0 mm, Q1 = 60 nC, Q2 = 80 nC, and q = 24 nC in the figure, what is the magnitude of the electric force on q?

A)2.7 N
B)1.9 N
C)2.3 N
D)1.5 N
E)0.52 N

Question 16

If a = 3.0 mm, b = 4.0 mm, Q1 = 60 nC, Q2 = −80 nC, and q = 36 nC in the figure, what is the magnitude of the electric force on q?

A)5.0 N
B)4.4 N
C)3.8 N
D)5.7 N
E)0.60 N

Question 17

Three point charges, two positive and one negative, each having a magnitude of 20 μC are placed at the vertices of an equilateral triangle (30 cm on a side). What is the magnitude of the electrostatic force on the negative charge?

A)80 N
B)40 N
C)69 N
D)57 N
E)75 N

Question 18

A point charge Q is placed on the x axis at x = 2.0 m. A second point charge, −Q, is placed at x = 3.0 m. If Q = 40 μC, what is the magnitude of the electrostatic force on a 30-μC charge placed at the origin?

A)7.2 N
B)3.9 N
C)1.5 N
D)14 N
E)8.1 N

Question 19

Three point charges, two positive and one negative, each having a magnitude of 20 μC are placed at the vertices of an equilateral triangle (30 cm on a side). What is the magnitude of the electrostatic force on one of the positive charges?

A)69 N
B)40 N
C)80 N
D)57 N
E)20 N

Question 20

Each of two small non-conducting spheres is charged positively, the combined charge being 40 μC. When the two spheres are 50 cm apart, each sphere is repelled from the other by a force of magnitude 2.0 N. Determine the magnitude of the smaller of the two charges.

A)1.4 μC
B)1.1 μC
C)2.0 μC
D)3.3 μC
E)17 μC

Question 21

An alpha particle (charge = +2e) is sent at high speed toward a gold nucleus (charge +79e). What is the electrical force acting on the alpha particle when it is at a distance of 2 × 10⁻¹⁴ m away from the gold nucleus? (e = 1.6 × 10⁻¹⁹ C)

Question 22

Three 2.50-μC charges are placed on tiny conducting spheres at the ends of 1.00 m-long strings that are connected at 120° angles as shown below. The magnitude, in N, of the force on the knot at the center is ​ ​

A)0.
B)3.75 × 10⁻².
C)5.63 × 10⁻².
D)6.50 × 10⁻².
E)7.50 × 10⁻².

Question 23

A charge of 50-μC is placed on the y axis at y = 3.0 cm and a 77-μC charge is placed on the x axis at x = 4.0 cm. If both charges are held fixed, what is the magnitude of the initial acceleration of an electron released from rest at the origin?

A)1.2 × 1020 m/s²
B)1.5 × 1020 m/s²
C)1.0 × 1020 m/s²
D)1.8 × 1020 m/s²
E)2.0 × 1020 m/s²

Question 24

Two identical pith balls supported by insulating threads hang side by side and close together, as shown below. One is positively charged; the other is neutral. We can conclude that

A)all field lines leaving the positively charged pith ball end on the neutral pith ball.
B)some of the field lines leaving the positively charged pith ball end on the neutral pith ball.
C)none of the field lines leaving the positively charged pith ball end on the neutral pith ball.
D)positive charge is transferred along the field lines until both balls have equal charges.
E)positive charge is transferred along the field lines until both balls hang along vertical lines.

Question 25

Two charged particles, Q1 and Q2, are a distance r apart with Q2 = 5Q1. Compare the forces they exert on one another when is the force Q2 exerts on Q1 and is the force Q1 exerts on Q2.

A) .
B) .
C) .
D) .
E) .

Question 26

Enrico says that positive charge is created when you rub a glass rod with silk, and that negative charge is simply the absence of positive charge. Rosetta says that negative charge is created and that positive charge is the absence of positive charge. (She has heard that Ben Franklin should have reversed the signs he associated with the charges.) Which one, if either, is correct?

A)Enrico, because there really is only one kind of charge.
B)Rosetta, because there really is only one kind of charge.
C)Neither: although no charge is present originally, both types of charge are created through friction.
D)Both: only one type of charge is created by friction at any one time.
E)Neither: both negative and positive charge are present simultaneously in all solid materials on Earth and the process described involves a transfer of charge, not the creation of charge.

Question 27

Three 2.50-μC charges are placed on tiny conducting spheres at the ends of 1.00 m-long strings that are connected at 120° angles as shown below. The magnitude, in N, of the force on any one of the charges is ​ ​

A)1.88 × 10⁻².
B)3.25 × 10⁻².
C)3.73 × 10⁻².
D)6.50 × 10⁻².
E)7.50 × 10⁻².

Question 28

Three pith balls supported by insulating threads hang from a support. We know that ball X is positively charged. When ball X is brought near balls Y and Z without touching them, it attracts Y and repels Z. Since pith is an insulating material, we can conclude that

A)Y has a negative charge.
B)Z has a negative charge.
C)Y has a positive charge.
D)Z has a positive charge.
E)Z is neutral (has no net charge).

Question 29

Imagine for a minute that the Moon is held in its orbit about the Earth by electrical forces rather than by gravitation. What electrical charges −Q on the Earth and +Q on the Moon are necessary to hold the Moon in a circular orbit with a period of 27.3 days? The Earth-Moon distance is 384,000 km and the mass of the Moon is 7.35 × 10²² kg.

Question 30

Rubber rods charged by rubbing with cat fur repel each other. Glass rods charged by rubbing with silk repel each other. A rubber rod and a glass rod charged respectively as above attract each other. A possible explanation is that

A)any two rubber rods charged this way have opposite charges on them.
B)any two glass rods charged this way have opposite charges on them.
C)a rubber rod and a glass rod charged this way have opposite charges on them.
D)all rubber rods always have an excess of positive charge on them.
E)all glass rods always have an excess of negative charge on them.

Question 31

Three 2.50-μC charges are placed on tiny conducting spheres at the ends of 1.00 m-long strings that are connected at 120° angles as shown below. The magnitude, in N, of the tension in any one of the strings is ​ ​

A)1.88 × 10⁻².
B)3.25 × 10⁻².
C)3.75 × 10⁻².
D)6.50 × 10⁻².
E)7.50 × 10⁻².

Question 32

Three pith balls supported by insulating threads hang from a support. We know that ball X is positively charged. When ball X is brought near balls Y and Z without touching them, it attracts Y and repels Z. Since pith is an insulating material, we can conclude that

A)Y has a negative charge.
B)Z has a negative charge.
C)Y has a positive charge.
D)Z is neutral (has no net charge).
E)Y is negatively charged or neutral (has no net charge).

Question 33

The symbol appears in Coulomb's law because we use independently defined units for

A)force and distance.
B)charge and distance.
C)distance and force.
D)force, distance, and electric charge.
E)charge.

Question 34

Two tiny metal spheres are fixed to the ends of a non-conducting string of length . Equal charges, +q, are placed on the metal spheres. Randall says that the force on the string has magnitude . Tilden says that the tension in the string has magnitude . Which one, if either, is correct?

A)Randall, because both charges exert forces on the string, but the tension is .
B)Tilden, because both charges exert forces on the string, but the net force is .
C)Both are correct, because both charges exert forces on the string.
D)Neither is correct, because both the tension and the force have magnitude .
E)Neither is correct, because the tension is , but the net force is 0.