Unit 8 Quiz #2 Targets 3-6

1. Electric force and gravitational force are alike in that both forces

Depend on charge

Depend on mass

Act only when objects are touching

Are field forces

Both electric force and gravitational force are field forces because they act on objects even when they are not in direct contact. These forces can act over a distance, without the need for physical contact between the objects involved. This is in contrast to forces like friction or tension, which require objects to be in contact for the force to be exerted. Therefore, the correct answer is that both electric force and gravitational force are field forces.

Explanation

Both electric force and gravitational force are field forces because they act on objects even when they are not in direct contact. These forces can act over a distance, without the need for physical contact between the objects involved. This is in contrast to forces like friction or tension, which require objects to be in contact for the force to be exerted. Therefore, the correct answer is that both electric force and gravitational force are field forces.

2. Objects become electrically charged as a result of the transfer of

Protons

Electrons

Neutrons

Nuclei

Objects become electrically charged as a result of the transfer of electrons. When electrons are transferred from one object to another, it creates an imbalance in the number of positive and negative charges, leading to the object becoming charged. Electrons are negatively charged particles, so when they are transferred, the object either gains or loses electrons, resulting in a net charge. This transfer of electrons is what causes objects to become electrically charged.

Explanation

Objects become electrically charged as a result of the transfer of electrons. When electrons are transferred from one object to another, it creates an imbalance in the number of positive and negative charges, leading to the object becoming charged. Electrons are negatively charged particles, so when they are transferred, the object either gains or loses electrons, resulting in a net charge. This transfer of electrons is what causes objects to become electrically charged.

3. The nucleus of an atom has _______________ electric charge.

A positive

A negative

A neutral

Both positive or negative

The nucleus of an atom has a positive electric charge because it contains protons, which are positively charged particles. The protons are balanced by an equal number of negatively charged electrons in the electron cloud surrounding the nucleus, resulting in an overall neutral charge for the atom.

Explanation

The nucleus of an atom has a positive electric charge because it contains protons, which are positively charged particles. The protons are balanced by an equal number of negatively charged electrons in the electron cloud surrounding the nucleus, resulting in an overall neutral charge for the atom.

4. Rubbing a balloon through dry hair gives the balloon a _______________ electric charge.

Positve

Negative

A neutral

Balanced

Rubbing a balloon through dry hair transfers electrons from the hair to the balloon. Electrons have a negative charge, so when the balloon gains electrons, it becomes negatively charged. Therefore, the correct answer is negative.

Explanation

Rubbing a balloon through dry hair transfers electrons from the hair to the balloon. Electrons have a negative charge, so when the balloon gains electrons, it becomes negatively charged. Therefore, the correct answer is negative.

5. An electric force F exists between two objects, both having the charge q. If the charge on one object is doubled to 2q, the force between the objects becomes

1/4 F

1/2 F

2 F

4 F

When the charge on one object is doubled from q to 2q, the force between the objects becomes 2 F. This is because the electric force between two charged objects is directly proportional to the product of their charges. Therefore, when the charge is doubled, the force also doubles.

Explanation

When the charge on one object is doubled from q to 2q, the force between the objects becomes 2 F. This is because the electric force between two charged objects is directly proportional to the product of their charges. Therefore, when the charge is doubled, the force also doubles.

6. Suppose you separate the electrons and protons in a gram of hydrogen and place the protons at Earth's North Pole and the electrons at Earth's South Pole. How much charge is at each pole if the magnitude of the electric force compressing Earth is 5.17 ´ 10⁵ N? Earth's diameter is 1.27 ´ 10⁷ m.

9.63 x 10^4 C

4.63 x 10^9 C

19.11 C

182.59 C

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Explanation

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7. A large pearl was found in the Philippines in 1934. Suppose the pearl is placed on a spring scale whose spring constant is 362 N/m. If the scale's platform oscillates with a frequency of 1.20 Hz, what is the mass of the pearl?

13.20 kg

6.37 kg

620.28 kg

1286.21 kg

The mass of the pearl can be determined using the formula for the period of a mass-spring system, which is T = 2π√(m/k), where T is the period, m is the mass, and k is the spring constant. Rearranging the formula to solve for m, we get m = (T^2 * k) / (4π^2). Plugging in the values given in the question, we have T = 1/1.20 = 0.833 s and k = 362 N/m. Substituting these values into the formula, we find m = (0.833^2 * 362) / (4π^2) ≈ 6.37 kg. Therefore, the mass of the pearl is 6.37 kg.

Explanation

The mass of the pearl can be determined using the formula for the period of a mass-spring system, which is T = 2π√(m/k), where T is the period, m is the mass, and k is the spring constant. Rearranging the formula to solve for m, we get m = (T^2 * k) / (4π^2). Plugging in the values given in the question, we have T = 1/1.20 = 0.833 s and k = 362 N/m. Substituting these values into the formula, we find m = (0.833^2 * 362) / (4π^2) ≈ 6.37 kg. Therefore, the mass of the pearl is 6.37 kg.

8. Which of the following best represents a difference between electric force and gravitational force?

Gravitational force is stronger than electric force.

Electric force can both attract and repel.

Electric force is inversely proportional to the square of the distance between objects.

Gravitational force exists between objects that are not touching.

The given answer is correct because electric force is unique in that it can both attract and repel objects. This is due to the fact that electric charges can be positive or negative, and like charges repel while opposite charges attract. In contrast, gravitational force only attracts objects and does not have the ability to repel. Therefore, the ability of electric force to both attract and repel is a key difference between electric force and gravitational force.

Explanation

The given answer is correct because electric force is unique in that it can both attract and repel objects. This is due to the fact that electric charges can be positive or negative, and like charges repel while opposite charges attract. In contrast, gravitational force only attracts objects and does not have the ability to repel. Therefore, the ability of electric force to both attract and repel is a key difference between electric force and gravitational force.

9. An electric force F exists between two objects separated from each other by distance r. If the distance is decreased to 0.5r, the force between the two objects becomes

1/4 F

1/2 F

2 F

4 F

When the distance between two objects decreases to 0.5r, the force between them becomes 4 times greater than the original force (4F). This is because the electric force is inversely proportional to the square of the distance between the objects. When the distance is halved, the denominator in the equation becomes 0.5^2 = 0.25, resulting in a force that is 4 times stronger.

Explanation

When the distance between two objects decreases to 0.5r, the force between them becomes 4 times greater than the original force (4F). This is because the electric force is inversely proportional to the square of the distance between the objects. When the distance is halved, the denominator in the equation becomes 0.5^2 = 0.25, resulting in a force that is 4 times stronger.

10. Two friends in France use a pendulum hanging from the world's highest railroad bridge to exchange messages across a river. One friend attaches a letter to the end of the pendulum and releases it so that the pendulum swings across the river to the other friend. The bridge is 130.0 m above the river. How much time is needed for the letter to make one swing across the river? Assume the river is 16.0 m wide.

22.87 sec

8.02 sec

11.43 sec

4.01 sec

The time it takes for the letter to make one swing across the river can be determined using the formula for the period of a simple pendulum. The period is given by the equation T = 2π√(L/g), where T is the period, L is the length of the pendulum, and g is the acceleration due to gravity. In this case, the length of the pendulum is the sum of the height of the bridge (130.0 m) and the width of the river (16.0 m), so L = 130.0 m + 16.0 m = 146.0 m. The acceleration due to gravity is approximately 9.8 m/s^2. Plugging these values into the equation, we get T = 2π√(146.0/9.8) ≈ 11.43 sec. Therefore, the correct answer is 11.43 sec.

Explanation

The time it takes for the letter to make one swing across the river can be determined using the formula for the period of a simple pendulum. The period is given by the equation T = 2π√(L/g), where T is the period, L is the length of the pendulum, and g is the acceleration due to gravity. In this case, the length of the pendulum is the sum of the height of the bridge (130.0 m) and the width of the river (16.0 m), so L = 130.0 m + 16.0 m = 146.0 m. The acceleration due to gravity is approximately 9.8 m/s^2. Plugging these values into the equation, we get T = 2π√(146.0/9.8) ≈ 11.43 sec. Therefore, the correct answer is 11.43 sec.