Deck 19: Electric Charges, Forces, and Fields

Question 1

In outer space,a positive charge q is released near a positive fixed charge Q,as shown in the figure.As q moves away from Q,what is true about the motion of q? (There may be more than one correct choice. )

A)It will move with decreasing speed.
B)It will move with constant acceleration.
C)It will move with increasing acceleration.
D)It will move with decreasing acceleration.
E)It will move with increasing speed.

Answer 1

It will move with decreasing acceleration.
It will move with increasing speed.

Question 2

A small charged plastic ball is vertically above another charged small ball in a frictionless test tube as shown in the figure.The balls are in equilibrium a distance d apart.If the charge on each ball is doubled,the equilibrium distance between the balls in the test tube would become

A) d.
B)2d.
C)4d.
D)8d.
E)d/4.

Answer 2

2d.

Question 3

Four point charges of varying magnitude and sign are arranged on the corners of the square of side d as shown in the figure.Which one of the arrows shown represents the net force acting on the point charge with a charge +Q?

A)A
B)B
C)C
D)D

Answer 3

A

Question 4

Electrically neutral objects cannot exert an electrical force on each other,but they can exert a gravitational force on each other.

Question 5

Two point charges,Q₁ and Q₂,are separated by a distance R.If the magnitudes of both charges are halved and their separation is also halved,what happens to the electrical force that each charge exerts on the other one?

A)It increases by a factor of 16.
B)It increases by a factor of 8.
C)It increases by a factor of 2.
D)It increases by a factor of 4.
E)It remains the same.

Question 6

X and Y are two initially uncharged metal spheres on insulating stands,and they are in contact with each other.A positively charged rod R is brought close to X as shown in part (a)of the figure.Sphere Y is now moved away from X,as shown in part (b).What are the final charge states of X and Y?

A)Both X and Y are neutral.
B)X is positive and Y is neutral.
C)X is neutral and Y is positive.
D)X is negative and Y is positive.
E)Both X and Y are negative.

Question 7

Three equal charges +Q are at three of the corners of a square of side d.A fourth charge +Q of equal magnitude is at the center of the square as shown in the figure Which one of the arrows shown represents the net force acting on the charge at the center of the square?

A)A
B)B
C)C
D)D

Question 8

Four point charges Q of equal magnitude and sign are arranged on three of the corners of the square of side d as shown in the figure Which one of the arrows shown represents the net force acting on the charge at the upper right hand corner of the square?

A)A
B)B
C)C
D)D

Question 9

Four point charges of equal magnitudes but with varying signs are arranged on three of the corners and at the center of the square of side d as shown in the figure.Which one of the arrows shown represents the net force acting on the center charge?

A)A
B)B
C)C
D)D

Question 10

A negatively-charged rod is brought close to (but does not touch)two neutral spheres that are in contact with each other but insulated from the ground.If the two spheres are then separated,what kind of charge will be on the spheres?

A)The sphere near the charged rod becomes positive and the other one becomes negative.
B)The sphere near the charged rod becomes negative and the other one becomes positive.
C)The spheres do not get any charge.
D)Both spheres become negative.
E)Both spheres become positive.

Question 11

Two very small plastic balls of equal mass are released from rest.One of them carries +10 µC of excess charge and the other one carries +1µC of charge.No other charges or fields are present.Which of the following statements are true about them as they move away from each other? (There may be more than one correct choice. )

A)The acceleration of the 10-µC ball is 10 times that of the 1-µC ball.
B)The acceleration of the 1-µC ball is 10 times that of the 10-µC ball.
C)The balls always have accelerations of equal magnitude.
D)The speed of the balls keeps increasing.
E)The acceleration of the balls keeps increasing.

Question 12

A hydrogen nucleus,which has a charge +e,is situated to the left of a carbon nucleus,which has a charge +6e.Which statement is true?

A)The electrical force experienced by the hydrogen nucleus is to the left,and the magnitude is equal to the force exerted on the carbon nucleus.
B)The electrical force experienced by the hydrogen nucleus is to the left,and the magnitude is greater than the force exerted on the carbon nucleus.
C)The electrical force experienced by the hydrogen nucleus is to the left,and the magnitude is less than the force exerted on the carbon nucleus.
D)The electrical force experienced by the hydrogen nucleus is to the right,and the magnitude is equal to the force exerted on the carbon nucleus.

Question 13

A plastic rod is charged up by rubbing a wool cloth,and brought to an initially neutral metallic sphere that is insulated from ground.It is allowed to touch the sphere for a few seconds,and then is separated from the sphere by a small distance.After the rod is separated,the rod

A)is repelled by the sphere.
B)is attracted to the sphere.
C)feels no force due to the sphere.

Question 14

Two uncharged metal spheres,#1 and #2,are mounted on insulating support rods.A third metal sphere,carrying a positive charge,is then placed near #2.Now a copper wire is momentarily connected between #1 and #2 and then removed.Finally,sphere #3 is removed.In this final state

A)spheres #1 and #2 are still uncharged.
B)sphere #1 carries positive charge and #2 carries negative charge.
C)sphere #1 carries negative charge and #2 carries positive charge.
D)spheres #1 and #2 both carry positive charge.
E)spheres #1 and #2 both carry negative charge.

Question 15

Two point charges,Q₁ and Q₂,are separated by a distance R.If the magnitudes of both charges are doubled and their separation is also doubled,what happens to the electrical force that each charge exerts on the other one?

A)It increases by a factor of 2.
B)It increases by a factor of .
C)It is reduced by a factor of .
D)It increases by a factor of 4.
E)It remains the same.

Question 16

Two identical small charged spheres are a certain distance apart,and each one initially experiences an electrostatic force of magnitude F due to the other.With time,charge gradually diminishes on both spheres by leaking off.When each of the spheres has lost half its initial charge,what will be the magnitude of the electrostatic force on each one?

A)1/16 F
B)1/8 F
C)1/4 F
D)1/2 F
E)1/ F

Question 17

If two objects are electrically attracted to each other,

A)both objects must be negatively charged.
B)both objects must be positively charged.
C)one object must be negatively charged and the other object must be positively charged.
D)the objects could be electrically neutral.
E)None of the above statements are absolutely true.

Question 18

Four point charges of equal magnitude but with varying signs are arranged on three of the corners and at the center of the square of side d as shown in the figure.Which one of the arrows shown represents the net force acting on the center charge?

A)A
B)B
C)C
D)D

Question 19

Two tiny beads are 25 cm apart with no other charges or fields present.Bead A carries 10 µC of charge and bead B carries 1 µC.Which one of the following statements is true about the magnitudes of the electric forces on these beads?

A)The force on A is 10 times the force on B.
B)The force on B is 10 times the force on A.
C)The force on A is exactly equal to the force on B.
D)The force on A is 100 times the force on B.
E)The force on B is 100 times the force on A.

Question 20

A negatively-charged plastic rod is brought close to (but does not touch)a neutral metal sphere that is connected to ground.After waiting a few seconds,the ground connection is removed (without touching the sphere),and after that the rod is also removed.The sphere is now

A)negatively charged.
B)positively charged.
C)neutral.

Question 21

The figure shows two unequal charges,+q and -Q.Charge -Q has greater magnitude than charge +q.Point X is midway between the charges.In what section of the line will there be a point where the resultant electric field is zero?

A)VW
B)WX
C)XY
D)YZ

Question 22

What is the charge on 1.0 kg of protons? (e = 1.60 × 10^-19 C,m_proton = 1.67 × 10^-27 kg)

A)1.0 C
B)1000 C
C)9.6 × 10⁷ C
D)6.0 × 10²⁶ C
E)6.0 × 10²³ C

Question 23

An asteroid of mass 58,000 kg carrying a negative charge of
Is
From a second asteroid of mass
Carrying a negative charge of
What is the magnitude of the net force the asteroids exert upon each other,assuming we can treat them as point particles? (G = 6.67 × 10^-11 N ∙ m²/kg²,k = 1/4 πε₀ = 8.99 × 10⁹ N ∙ m²/C²)

A)0.000040 N
B)0.0062 N
C)570,000 N
D)510,000 N

Question 24

The figure shows electric field lines arising from two small charged particles P and Q.Consider the following two statements:
(i)The charge on P is smaller than the charge on Q.
(ii)The electrostatic force on P is smaller than the force on Q.
Which of the above statements are true?

A)Only (i)is true.
B)Only (ii)is true.
C)Both (i)and (ii)are true.
D)Neither (i)nor (ii)is true.

Question 25

An electron and a proton are released simultaneously from rest and start moving toward each other due to their electrostatic attraction,with no other forces present.Which of the following statements are true just before they are about to collide? (There could be more than one correct choice. )

A)They are closer to the to the initial position of the electron that to the initial position of the proton.
B)They are closer to the to the initial position of the proton that to the initial position of the electron.
C)They are at the midpoint of their initial separation.
D)They both have the same speed.
E)The electrostatic force on the proton is greater than the electrostatic force on the electron.

Question 26

A conductor is placed in a steady external electric field.Which of the following statements are correct for this situation? (There could be more than one correct choice. )

A)The electric field is zero inside the conductor.
B)All the free electrons go to the surface of the conductor.
C)The surface of the conductor is neutral.
D)The electric field just outside the surface of the conductor is perpendicular to the surface.
E)None of the above statements are correct.

Question 27

The force of attraction that a -40.0 μC point charge exerts on a +108 μC point charge has magnitude 4.00 N.How far apart are these two charges? (k = 1/4πε₀ = 8.99 × 10⁹ N ∙ m²/C²)

A)2.10 m
B)3.67 m
C)3.12 m
D)2.49 m
E)1.13 m

Question 28

Which one of the arrows shown in the figure best represents the direction of the electric field between the two uniformly charged metal plates?

A)A
B)B
C)C
D)D
E)None of the above

Question 29

An electron is initially moving to the right when it enters a uniform electric field directed upwards,as shown in the figure.Which trajectory (X,Y,Z,or W)will the electron follow in the field?

A)trajectory W
B)trajectory X
C)trajectory Y
D)trajectory Z

Question 30

Four tiny charged particles (two having a charge +Q and two having a charge -Q)are distributed on the x- and y-axes as shown in the figure.Each charge is equidistant from the origin.In which direction is the net electric field at the point P on the y-axis?

A)directly up (in the +y direction)
B)directly left (-x direction)
C)upwards and towards the left
D)upwards and towards the right
E)The net field is zero,so there is no direction.

Question 31

Three equal-magnitude point charges of varying signs are placed at the corners of a square of side d as shown in the figure.Which one of the arrows shown represents the direction of the net electric field at the center of the square?

A)A
B)B
C)C
D)D

Question 32

Three equal-magnitude point charges of varying signs are placed at three of the corners of a square of side d as shown in the figure.Which one of the arrows shown represents the direction of the net electric field at the vacant corner of the square?

A)A
B)B
C)C
D)D

Question 33

Three equal negative point charges -q are placed at three of the corners of a square of side d as shown in the figure.Which one of the arrows shown represents the direction of the net electric field at the center of the square?

A)A
B)B
C)C
D)D

Question 34

If a charge generator builds a negative static charge of - 7.00µC. How many electrons are transferred to it during this process.(e = 1.60 × 10^-19C)

A)4.38 × 10¹³
B)7.0
C)1.12 × 10^-18
D)43.8

Question 35

Two electrons are
Apart at closest approach.What is the magnitude of the maximum electric force that they exert on each other? (e = 1.60 × 10^-19 C,k = 1/4πε₀ = 9.0 10⁹ N ∙ m²/C²)

A)5.8 × 10^-25 N
B)2.3 × 10¹⁰ N
C)2.3 N
D)5.8 × 10^-27 N

Question 36

The electric field at point P due to a point charge Q a distance R away from P has magnitude E.In order to double the magnitude of the field at P,you could

A)double the distance to 2R.
B)double the charge to 2Q.
C)reduce the distance to R/2.
D)reduce the distance to R/4.
E)double the charge to 2Q and at the same time reduce the distance to R/2.

Question 37

Two stationary point charges q₁ and q₂ are shown in the figure along with a sketch of some field lines representing the electric field produced by them.What can you deduce from the sketch?

A)q₁ is negative and q₂ is positive;the magnitudes are equal.
B)q₁ and q₂ have the same sign;the magnitudes are equal.
C)q₁ is positive and q₂ is negative;the magnitude of q₁ is greater than the magnitude of q₂.
D)q₁ is negative and q₂ is positive;the magnitude of q₁ is less than the magnitude of q₂.
E)q₁ and q₂ have the same sign;the magnitude of q₁ is greater than the magnitude of q₂.

Question 38

Three equal positive point charges +q are placed at the corners of a square of side d as shown in the figure.Which one of the arrows shown represents the direction of the net electric field at the center of the square?

A)A
B)B
C)C
D)D

Question 39

A solid aluminum cube rests on a wooden table in a region where a uniform external electric field is directed straight upward.What can we say concerning the charge on the top surface of the cube?

A)The top surface is charged positively.
B)The top surface is charged negatively.
C)The top surface is neutral.
D)The top surface's charge cannot be determined without further information.

Question 40

Three equal negative point charges -q are placed at three of the corners of a square of side d as shown in the figure.Which one of the arrows shown represents the direction of the net electric field at the vacant corner of the square?

A)A
B)B
C)C
D)D

Question 41

Two 10¢ coins (dimes)carrying identical charges are lying 2.5 m apart on a table.If each of these coins experiences an electrostatic force of magnitude 2.0 N due to the other coin,how large is the charge on each coin? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²)

A)2.6 μC
B)26 μC
C)6.7 μC
D)5.2 μC
E)52 μC

Question 42

Two equally charged tiny spheres of mass 1.0 g are placed 2.0 cm apart.When released,they begin to accelerate away from each other at
What is the magnitude of the charge on each sphere,assuming only that the electric force is present? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²)

A)140 nC
B)120 nC
C)95 nC
D)75 nC

Question 43

As shown in the figure,the charge Q is midway between two other charges.If
What must be the charge q1 so that charge q2 remains stationary as Q and q1 are held in place?

A)30 nC
B)15 nC
C)7.5 nC
D)60 nC

Question 44

As shown in the figure,three small charges are equally spaced on the arc of a circle that is centered at the charge Q,where Q = +23 nC and all the other quantities are accurate to two significant figures.What is the magnitude of the net electric force on the charge Q due to the other three charges? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²)

A)2.6 × 10^-4 N
B)1.7 × 10^-4 N
C)2.1 × 10^-4 N
D)3.1 × 10^-4 N

Question 45

When 1.0-µC point charge is 15 m from a second point charge,the force each one experiences a force of 1.0 µN.What is the magnitude of the second charge? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²)

A)25 C
B)1.0 C
C)10 nC
D)0.025 C
E)25 nC

Question 46

Suppose you wanted to hold up an electron against the force of gravity by the attraction of a fixed proton some distance above it.How far above the electron would the proton have to be? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²,e = 1.6 × 10^-19 C,m_proton = 1.67 × 10^-27 kg,m_electron = 9.11 × 10^-31 kg)

A)1.5 m
B)2.3 m
C)3.7 m
D)4.6 m
E)5.1 m

Question 47

Two point charges each experience a 1-N electrostatic force when they are 2 cm apart.If they are moved to a new separation of 8 cm,what is the magnitude of the electric force on each of them?

A)2 N
B)1/2 N
C)1/4 N
D)1/8 N
E)1/16 N

Question 48

One point charge +Q is placed at the center of a square,and a second point charge -Q is placed at the upper-left corner of the square.It is observed that an electrostatic force of magnitude 2.0 N acts on the positive charge at the center.Now a third charge -Q is placed at the lower-left corner of the square,as shown in the figure.What is the magnitude of the net force that acts on the center charge now?

A)0.0 N
B)2.8 N
C)4.0 N
D)5.3 N

Question 49

The zirconium nucleus contains 40 protons,and an electron is 1.0 nm from the nucleus.What is the electric force on the electron due to the nucleus? ( e = 1.60 × 10^-19 C,k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²)

A)2.9 nN
B)1000 C
C)3.7 nN
D)6.8 nN
E)9.2 nN

Question 50

A particle of charge +2q is placed at the origin and particle of charge -q is placed on the x-axis at x = 2a.Where on the x-axis can a third positive charge be placed so that the net electric force on it is zero?

A)3.4a
B)6.8a
C)8.6a
D)9.3a
E)1.0a

Question 51

Two tiny beads,each of mass 3.2 g,carry equal-magnitude charges.When they are placed 6.4 cm apart and released in outer space,they begin to accelerate toward each other at 538 m/s².What is the magnitude of the charge on each bead? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²)

A)510 nC
B)44 nC
C)1800 nC
D)890 nC
E)1300 nC

Question 52

Two tiny particles carrying like charges of the same magnitude are
Apart.If the electric force on one of them is
What is the magnitude of the charge on each of these particles? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²)

A)2.4 × 10^-2 C
B)2.4 × 10^-8 C
C)4.5 × 10⁴ C
D)2.4 × 10^-5 C

Question 53

Three identical 3.0-µC charges are placed at the vertices of an equilateral triangle that measures 30 cm on a side.What is the magnitude of the electrostatic force on any one of the charges? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²)

A)1.6 N
B)1.8 N
C)2.0 N
D)2.2 N
E)2.4 N

Question 54

A proton is located at the point (x = 1.0 nm,y = 0.0 nm)and an electron is located at the point (x=0.0nm, y= 4.0nm). Find the magnitude of the electrostatic force that each one exerts on the other.(k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²,e = 1.6 × 10^-19C)

A)1.4 × 10^-11 N
B)5.3 × 10^-18 N
C)5.3 × 10⁸ N
D)5.9 × 10^-15 N

Question 55

The three point charges +4.0 μC,-5.0 μC,and -9.0 μC are placed on the x-axis at the points x = 0 cm,x = 40 cm,and x = 120 cm,respectively.What is the x component of the electrostatic force on the -9.0 μC charge due to the other two charges? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²)

A)-0.55 N
B)0.55 N
C)0.64 N
D)0.41 N
E)-0.41 N

Question 56

Two tiny particles having charges of +5.00 μC and +7.00 μC are placed along the x-axis.The +5.00-µC particle is at x = 0.00 cm,and the other particle is at x = 100.00 cm.Where on the x-axis must a third charged particle be placed so that it does not experience any net electrostatic force due to the other two particles?

A)4.58 cm
B)45.8 cm
C)50 cm
D)9.12 cm
E)91.2 cm

Question 57

As shown in the figure,three charges are at corners of a rectangle.The charge in the bottom right corner is Q = - 90 nC,and all the other quantities are accurate to two significant figures.What is the magnitude of the net electrical force on Q due to the other two charges? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²)

A)3.8 × 10^-2 N
B)2.8 × 10^-2 N
C)5.3 × 10^-2 N
D)7.1 × 10^-2 N

Question 58

As shown in the figure,three charges are at the vertices of an equilateral triangle.The charge Q is 6.7 nC,and all the other quantities are accurate to two significant figures.What is the magnitude of the net electric force on the charge Q due to the other two charges? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²)

A)2.1 × 10^-3 N
B)1.2 × 10^-3 N
C)1.0 × 10^-3 N
D)1.4 × 10^-3 N

Question 59

Two tiny particles having charges of +7.00 μC and -9.00 μC are placed along the y-axis.The +7.00-µC particle is at y = 0.00 cm,and the other particle is at y = 40.00 cm.Where must a third charged particle be placed along the y-axis so that it does not experience any net electric force due to the other two particles?

A)0.200 m
B)2.99 m
C)-0.187 m
D)-2.99 m
E)0.187 m

Question 60

Three point charges are located on the x-axis at the following positions: Q₁ = +2.00 μC is at x = 1.00 m,Q₂ = +3.00 μC is at x = 0.00,and Q₃ = -5.00 μC is at x = -1.00 m.What is the magnitude of the electric force on Q2? (k = 1/4πε₀ = 8.99 × 10⁹ N ∙ m²/C²)

A)0.0540 N
B)0.135 N
C)0.158 N
D)0.0810 N
E)0.189 N

Question 61

What is the magnitude of the electric field 2.8 cm from a tiny object that carries an excess charge of -16 nC? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²)

A)180,000 N/C
B)5100 N/C
C)1.8 × 10¹⁴ N/C
D)-180,000 N/C
E)-5100 N/C

Question 62

A small object with a 5.0-μC charge is accelerating horizontally on a friction-free surface at 0.0050 m/s2 due only to an electric field.If the object has a mass of 2.0 g,what is the magnitude of the electric field?

A)2.0 N/C
B)4.0 N/C
C)0.0020 N/C
D)0.0040 N/C
E)1.0 N/C

Question 63

The figure shows two tiny 5.0-g spheres suspended from very light 1.0-m-long threads.The spheres repel each other after each one is given the same positive charge and hang at rest when θ = 4.1°.What is the charge on each sphere? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²)

A)22 nC
B)89 nC
C)360 nC
D)180 nC
E)45 nC

Question 64

The electric field at a point 2.8 cm from a small object points toward the object with a strength of 180,000 N/C.What is the object's charge q? (k = 1/4πε₀ = 8.99 × 10⁹ N ∙ m²/C²)

A)-16 nC
B)+16 nC
C)-17 nC
D)+17 nC

Question 65

A small glass bead has been charged to 1.9 nC.What is the strength of the electric field 2.0 cm from the center of the bead? (k = 1/4πε₀ = 8.99 × 10⁹ N ∙ m²/C²)

A)4.3 × 10⁴ N/C
B)8.5 × 10² N/C
C)8.1 × 10^-5 N/C
D)8.5 × 10^-7 N/C

Question 66

An electron is projected with an initial velocity v₀ = 8.4 ×
M/s along the y-axis,which is the centerline between a pair of charged plates,as shown in the figure.The plates are 1.0 m long and are separated by 0.10 m.A uniform electric field of magnitude E in the +x-direction is present between the plates.If the magnitude of the acceleration of the electron is measured to be
What is the magnitude of the electric field between the plates? (e = 1.6 × 10^-19 C,m_electron = 9.11 × 10^-31 kg)

A)51,000 N/C
B)45,000 N/C
C)40,000 N/C
D)35,000 N/C
E)29,000 N/C

Question 67

Two tiny particles having charges +20.0 μC and -8.00 μC are separated by a distance of 20.0 cm.What are the magnitude and direction of electric field midway between these two charges? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²)

A)25.2 × N/C directed towards the negative charge
B)25.2 × N/C directed towards the positive charge
C)25.2 × N/C directed towards the negative charge
D)25.2 × N/C directed towards the positive charge
E)25.2 × N/C directed towards the negative charge

Question 68

A pair of charged conducting plates produces a uniform field of 12,000 N/C,directed to the right,between the plates.The separation of the plates is 40 mm.An electron is projected from plate A,directly toward plate B,with an initial speed of v₀ = 2.0 × 10⁷ m/s.What is the speed of the electron as it strikes plate B?
,m_electron = 9.11 × 10^-31 kg)

A)1.2 × 10⁷ m/s
B)1.5 × 10⁷ m/s
C)1.8 × 10⁷ m/s
D)2.1 × 10⁷ m/s
E)2.4 × 10⁷ m/s

Question 69

A small 0.050-kg insulating sphere carries a charge of -60 μC and is hanging by a vertical silk thread from a fixed point in the ceiling.An external uniform vertical electric field is now applied.If the applied electric field has a magnitude of 3000 N/C and is directed downward,what is the tension in the silk thread? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²)

A)0.19 N
B)0.31 N
C)0.41 N
D)0.52 N
E)0.71 N

Question 70

What is the magnitude of a the vertical electric field that will balance the weight of a plastic sphere of mass
That has been charged to -3.0 nC? (k = 1/4πε₀ = 9.0 × 10⁹ N ∙ m²/C²)

A)6.9 × 10⁶ N/C
B)7.8 × 10⁵ N/C
C)1.5 × 10⁶ N/C
D)2.1 × 10⁶ N/C

Question 71

A small styrofoam ball of mass 0.120 g is placed in an electric field of 6000 N/C pointing downward.What excess charge must be placed on the ball for it to remain suspended in the field?

A)-16.0 nC
B)-18.0 nC
C)-57.2 nC
D)-125 nC
E)-196 nC

Question 72

A +5.0-μC point charge is placed at the 0 cm mark of a meter stick and a -4.0-μC charge is placed at the 50 cm mark.What is the net electric field at the 30 cm mark? (k = 1/4πε₀ = 8.99 × 10⁹ N ∙ m²/C²)

A)4.0 × 10⁵ N/C
B)5.0 × 10⁵ N/C
C)9.0 × 10⁵ N/C
D)1.4 × 10⁶ N/C

Question 73

A particle with a charge of +4.0 μC has a mass of 5.0 g.What magnitude electric field directed upward will exactly balance the weight of the particle?

A)4.1 × 10⁴ N/C
B)8.2 × 10⁴ N/C
C)4.4 × 10⁴ N/C
D)1.2 × 10⁴ N/C
E)5.1 × 10⁴ N/C

Question 74

A +5.00-μC point charge is placed at the 0.0 cm mark of a meter stick and a -4.00-μC point charge is placed at the 50.0 cm mark.At what point on a line through the ends of the meter stick is the electric field equal to zero?

A)1.4 m from the 0 cm mark
B)2.5 m from the 0 cm mark
C)2.9 m from the 0 cm mark
D)3.3 m from the 0 cm mark
E)4.7 m from the 0 cm mark

Question 75

A proton is placed in an electric field of intensity 800 N/C.What are the magnitude and direction of the acceleration of the proton due to this field? (e = 1.60 × 10^-19 C,m_proton = 1.67 × 10^-27 kg)

A)7.66 × m/
opposite to the electric field
B)7.66 × m/
opposite to the electric field
C)7.66 × m/
in the direction of the electric field
D)76.6 × m/
opposite to the electric field
E)76.6 × m/
in the direction of the electric field