Two uncharged metal spheres, spaced 25.0 cm apart, have a capacitance of 26.0 pF. How much work would it take to move 12.0 nC of charge from one sphere to the other? Answer in Joules.

Answers

Answer 1

Answer:

[tex]W=2.76\times 10^{-6}\ J[/tex]

Explanation:

Given that,

The distance between two spheres, r = 25 cm = 0.25 m

The capacitance, C = 26 pF = 26×10⁻¹² F

Charge, Q = 12 nC = 12 × 10⁻⁹ C

We need to find the work done in moving the charge. We know that, work done is given by :

[tex]U=\dfrac{Q^2}{2C}[/tex]

Put all the values,

[tex]U=\dfrac{(12\times 10^{-9})^2}{2\times 26\times 10^{-12}}\\\\U=2.76\times 10^{-6}\ J[/tex]

So, the work done is [tex]2.76\times 10^{-6}\ J[/tex].


Related Questions

When the Glen Canyon hydroelectric power plant in Arizona is running at capacity, 690 m3m3 of water flows through the dam each second. The water is released 220 mm below the top of the reservoir. If the generators that the dam employs are 90% efficient, what is the maximum possible electric power output?

Answers

Answer:

The output electric power is 1338876 W.

Explanation:

Volume, V = 690 cubic meter

height, h = 220 mm = 0.22 m

efficiency = 90 %

time , t = 1 s

Let the mass is m.

m = volume x density  

m = 690 x 1000 = 690000 kg

The input power is

P = m g h = 690000 x 9.8 x 0.22 = 1497640 W

The electric power out put is

[tex]P' = 90 % of 1487640\\\\\\P' = 1338876 W[/tex]

What innovation did jethro wood add to plows in the 1800s?

Answers

Built by 1800, it was the home of inventor Jethro Wood (1774-1834), whose 1819 invention of an iron moldboard plow revolutionized American agriculture.

Fiber optic (FO) cables are based upon the concept of total internal reflection (TIR), which is achieved when the FO core and cladding have the same refractive indices.

a. True
b. False

Answers

Answer:

False

Explanation:

Though fiber active cable is based on the concept of internal reflection but it is achieved by refractive index which transmit data through fast traveling pulses of light. It has a layer of glass and insulating casing called “cladding,”and this is is wrapped around the central fiber thereby causing light to continuously bounce back from the walls of the Cable.

Falls often cause injuries, so one of the significant aspects of falls is the displacement and motion of a body. It is defined as how far a body moves vertically during the fall. Accordingly, there are three important factors that should be known to compute the kinetic energy (KE) of a falling body. These factors are:

Answers

Answer:

We need, mass, gravity and height.

Explanation:

When a body falls freely from a height, its initial velocity is zero, but due to the height it has some potential energy at the top and the kinetic energy is zero.

As it falls, the potential energy is gradually converted in to the kinetic energy so that the total energy of the falling body is conserved.

At the time as the body strikes the ground, the entire potential energy is converted into the kinetic energy.

Potential energy is given by

U = m g h

where, m is the mass, g is the gravity and h is the height,

So, to get the kinetic energy we require mass, gravity and height of the body.

A major artery with a 1.3 cm^2 cross-sectional area branches into 18 smaller arteries, each with an average cross-sectional area of 0.6 cm^2. By what factor is the average velocity of the blood reduced when it passes into these branches?

Answers

Answer:

When the blood passes into the smaller branches, its average velocity reduces by a factor of 0.12

Explanation:

Given;

initial area of the artery, A₁ = 1.3 cm²

Area of each smaller 18 arteries, a₂ = 0.6 cm²

Total area of the smaller 18 arteries, A₂ = 18 x 0.6 cm²

Apply flow rate equation;

Q = AV

where;

Q is the flow rate of the blood

V is the average velocity of the blood

If the flow rate is constant, then;

A₁V₁ = A₂V₂

[tex]V_2 = \frac{A_1V_1}{A_2} = \frac{1.3\times V_1}{18\times 0.6} \\\\V_2 = 0.12 \ V_1[/tex]

When the blood passes into the smaller branches, its average velocity reduces by a factor of 0.12

Phát biểu nào sau đây là SAI?
A. Cường độ điện trường là đại lượng
đặc trưng cho điện trường về phương
diện tác dụng lực.
B. Điện trường tĩnh là điện trường có
cường độ E không đổi tại mọi điểm.
C. Đơn vị đo cường độ điện trường là
vôn trên mét (V/m).
D. Trong môi trường đẳng hướng,
cường độ điện trường giảm  lần so với
trong chân không

Answers

Answer:

B.

Explanation:

sana makatulong sayo

Determine the values of m and n when the following average magnetic field strength of the Earth is written in scientific notation: 0.0000451 T. Enter m and n, separated by commas.

Answers

Answer:

B = 4.51×10⁻⁵ T

Explanation:

Given that,

The average magnetic field strength of the Earth is 0.0000451 T.

We need to write the value in the form of scientific notation. Any number in scientific notation is written as follows :

N=a×bⁿ

Where

n is any integer and a is a real no

So,

0.0000451 = 4.51×10⁻⁵ T

So, the required answer is equal to 4.51×10⁻⁵ T.

Given that average speed is distance traveled divided by time, determine the values of m and n when the time it takes a beam of light to get from the Sun to the Earth (in s) is written in scientific notation. Note: the speed of light is approximately 3.0×108 m/s. Enter m and n, separated by commas.

Answers

Answer:

[tex]5,2[/tex]

Explanation:

From the question we are told that:

Speed of light [tex]C=3.0×10^8 m/s.[/tex]

Generally the equation for Average Speed is mathematically given by

[tex]V_{avg}=\frac{d}{t}[/tex]

Where

d=Distance between the Earth and the sun

[tex]d=1.5*10^11m[/tex]

Therefore

[tex]t=\frac{d}{V_{avg}}[/tex]

[tex]t=\frac{1.5*10^11m}{3.0×10^8 m/s.}[/tex]

[tex]t=5*10^2s[/tex]

Since m and n is given in the form of

[tex]m*10^n[/tex]

Therefore

[tex]m=5 & n=2[/tex]

[tex]5,2[/tex]

A pair of butterflies reproduces and has one thousand offspring. All one thousand of the offspring have the alleles Aa. What is the most likely combination of alleles (genotype) for each parent?

Answers

Answer:

Alleles AA and aa

Explanation:

For all the offsprings of the butterflies to have the same heterozygous alleles Aa, it means the two parents have different homogyzous alleles. That is, one of the parents had the alleles AA while the other had the alleles aa. Thus, a combination of the two pairs of alleles will produce 100% Aa alleles in the offspring as seen in the image attached.

a car increases its speed as it moves across the floor. which form of energy is increasing for the car?

Answers

Answer:

kinetic

Explanation:

i just remember it from last year

Answer:

kinetic energy

Explanation:

expression for kinetic energy is

kinetic energy = (1/2) × mass × (velocity)^2

so , as velocity increases K.E increases

Match each term to the best description

a. Coefficient of friction
b. Friction
c. Kinetic friction
d. Normal
e. Static friction

1. A force that acts parallel to the surface.
2. A force that acts perpendicular to the surface.
3. A force that increases as applied force increases up to some maximum value
4. Magnitude depends on the interacting materials
5. A force that is constant regardless of the applied force

Answers

Answer:

Coefficient of friction =  Magnitude depends on the interacting materials

Friction = A force that acts parallel to the surface.

kinetic friction = A force that is constant regardless of the applied force

Normal = A force that acts perpendicular to the surface

Static friction = A force that increases as applied force increases up to some maximum value

Explanation:

Let's define all the forces, and then let's solve the problem.

Normal force:

When an object rests on some place (like a book on the table) the force that causes the book to not fall through the table is called the normal force, which is usually equal to the weight of the object and acts perpendicular to the surface where the object is resting.

Friction force.

When an object moves (or tries to move) parallel to a surface, such that the object is in contact with that surface, there appears a force that opposes to the movement (the force is parallel to the surface, and in the opposite direction to the movement).

And this force can be written as:

F = -N*μ

Where μ is the coefficient of friction and N is the normal force.

If the object is not moving yet (but there is applied a force that would move the object) the coefficient is called the coefficient of static friction which increases in a given range, until it can't keep increasing and the object starts to move, while if the object is moving, the coefficient is called the coefficient of kinetic friction and it is constant, where usually the first one is larger than the second, and these coefficients depend on both materials, the surface one and the object one.

Then we have two friction forces, one called the kinetic friction and the other called the static friction.

Then:

Coefficient of friction =  Magnitude depends on the interacting materials

Friction = A force that acts parallel to the surface.

kinetic friction = A force that is constant regardless of the applied force

Normal = A force that acts perpendicular to the surface

Static friction = A force that increases as applied force increases up to some maximum value

Magnetic fields can affect... (Check all that apply)
A. ...the motion of electrically charged particles.
B. ...the acceleration of small objects with mass.
C. ...the speed of light near the magnetic field.
D. ...the date we begin daylight savings time.
E. ...the direction compass needles point.
F. ...the electric current in nearby wires.

Answers

Answer:

A. the motion of electrically charged particles

The volume of a liquid is 830m'at 30°C and it is 850m'at 90°C. The
coefficient of volume expansion of the liquid is​

Answers

Answer:

4.02×10⁻⁴ K⁻¹

Explanation:

Applying,

γ = (v₂-v₁)/(v₁Δt)................. Equation 1

Where γ  = coefficient of volume expansion, v₂ = Final volume, v₁ = initial volume, Δt = change in temperature.

From the question,

Given: v₂ = 850 m³, v₁ = 830 m³, Δt = (90-30) = 60°C

Substitute these values into equation 1

γ  = (850-830)/(830×60)

γ  = 20/(830×60)

γ  = 4.02×10⁻⁴ K⁻¹

Got it never mind. The only reason I'm typing more is to fill out the required space

Answers

Answer:

hey. i dont know what you tryna say but if u replying to someone else, you should use the comments section. in that way you won't lose points.

The lumberjack pulls on the sled with 40 N at an angle of 30 degrees, pulling so the sled moves at a constant velocity. 1) What is the x component of the applied force? 2) What is the y component of the applied force? 3) If the loaded sled has a mass of 65 kg, what is the magnitude of the force of gravity? 4) What is the magnitude of the normal force acting on the sled? 5) What is the coefficient of friction between the snow and the sled?

Answers

1) (40 N) cos(30°) ≈ 34.6 N

2) (40 N) sin(30°) = 20 N

3) (65 kg) g = (65 kg) (9.80 m/s²) = 585 N

4) The net force on the sled acting in the vertical direction is made up of

• the sled's weight, 585 N, pointing downward

• the vertical component of the applied force, 20 N, pointing upward

• the normal force, with magnitude n, also pointing upward

The sled does not move up or down, so by Newton's second law,

F = n + 20 N - 585 N = 0   ==>   n = 565 N

5) The net force in the horizontal direction consists of

• the horizontal component of the applied force, 34.6 N, acting in the direction the sled's movement (call this the positive direction)

• kinetic friction, with magnitude f, pointing in the opposite and negative direction

By Newton's second law,

F = 34.6 N - f = 0   ==>   f ≈ 34.6 N

Now if µ is the coefficient of kinetic friction, then

f = µn   ==>   µ = f/n = (34.6 N) / (565 N) ≈ 0.0613

The component of the force is the effective part of that force in that direction.

What is the component of a force?

The component of the force is the effective part of that force in that direction.

1) The horizontal component of a force = 40 N cos 30 degrees = 34.6 N

2) The vertical component of the force = 40 N sin 30 degrees = 20 N

3) The magnitude of the gravitational force = mg cos 30 degrees  = 65 Kg * 9.8 m/s^2 * cos 30 degrees = 551.7 N

4) The normal force = 551.7 N

5) The coefficient of friction = F/R =  40 N /551.7 N = 0.07

Learn more about component of a force:https://brainly.com/question/15529350

#SPJ6

How does exhailing remove waste from the body? Explain the systems that make this happen‚ using complete sentences​

Answers

When we exhale, 90% waste material is Carbon Dioxide ( CO2 ) , so, it gets exhaled out in the form of CO2 rich air and it gets removed from the body, therefore our internal body becomes more pure and helps in making our internal temperature constant at a suitable level.

A test charge of -1.4 x 10-7 coulombs experiences a force of 5.4 x 10-1 newtons. Calculate the magnitude of the electric field created by the
negative test charge.
ОА.
1.4 x 106 newtons/coulomb
ОВ.
1.9 x 106 newtons/coulomb
OC. 5.4 x 10-1 newtons/coulomb
OD
3.6 x 106 newtons/coulomb

Answers

Answer:

3.86×10⁶ Newton/coulombs

Explaination:

Applying,

E = F/q....................... Equation 1

Where E = Electric Field, F  = Force, q = charge.

From the question,

Given: F = 5.4×10⁻¹ N, q = -1.4×10⁻⁷ coulombs

Substitute these values into equation 1

E = 5.4×10⁻¹/ -1.4×10⁻⁷

E = -3.86×10⁶ Newtons/coulombs

Hence the magnitude of the electric field created by the

negative test charge is 3.86×10⁶ Newton/coulombs

A conductor is placed in an external electrostatic field. The external field is uniform before the conductor is placed within it. The conductor is completely isolated from any source of current or charge.

1. Which of the following describes the electricfield inside this conductor?

a. It is in thesame direction as the original external field.
b. It is in theopposite direction from that of the original externalfield.
c. It has adirection determined entirely by the charge on itssurface.
d. It is alwayszero.

2. The charge density inside theconductor is:

a. 0
b. non-zero;but uniform
c. non-zero;non-uniform
d. infinite

Answers

Answer:pp

Explanation:

ii

what is the meanjng of laritude ??​

Answers

I’m assuming you meant latitude:

The angular distance north or south of the earth's equator, measured in degrees along a meridian, as on a map or globe.

a region based on its distance to the equator uses latitude measurements

basically: up and down , north to south from a certain point

If a duster is left on the top of the chalkboard, it is said to possess kinetic energy.

Answers

Answer:

In the above diagram, we move by horizontally with a velocity to the right. But due to gravity the hand falls a distance as we move .

Therefore the time it takes to fall by a distance is given by =.

If = as →∞, then from the laws of motion

=12()22

Therefore for the whole journey from left to right our muscle has to give a beat up at an amount equal to the gravity force. So, the work supplied by the muscle for one trip would be

∫=∫012()22

A man is going to rub the chalk off a blackboard, he is going to choose a way to rub off the chalk in two ways

Starting from the upper left corner of the board and moving horizontally to the right and moving slightly down and then again moving to the right and then when it reaches the left corner and so on

The second way is given in the following: He starts at the top and rubs down and then up again and so on.

He is going to choose the way that is less tiring in his arms. i.e., less work done by his muscles!

Somehow from vague intuitive notion I am inclined to agree that it would be less tiring to rub off the chalk if he moves the duster beginning at the top and rubbing horizontally and gradually decreasing the height when one reach the corners till everything is off.

I tried to calculate the muscle work by considering the following ideas(please correct me if I'm wrong):

The nerves inside our muscle has to fire its signal continuously throughout the entire interval of the process of rubbing and its has to oppose the gravitational force keeping the hand up the air.

When the hand is at the highest point on the blackboard, the muscle has to work against gravity =, as the muscle continues to work against gravity throughout the interval from left to right (the horizontal path of the first case) I couldn't find the total work withstood by our muscle.

A physical system is in the state |α> = cos(α)|+> + sin(α)|->. Two observables  = a(|+><+| + |-><-|) + b(|+><-| + |-><+|) e B = a(|+><+| - |-><-|) are measured. Check the uncertainty relationship for these two operators.

Answers

Answer:

sorry dear

Explanation:

sorry dear but ur question is hard to understand can u try to edit it so i can tell u the answer?

A car is travelling at 30m/s and decelerates [with normal car brakes, no trick] at 5m/s/s for 10 s. What is the car's final speed *
A) zero
B) -50m/s
C) -20m/s
D) Not possible to tell
show your full work

Answers

Answer:

B. -20 m/s

Explanation:

Given the following data:

Initial velocity = 30 m/s

Acceleration = 5 m/s²

Deceleration = -5 m/s² (deceleration is the negative of acceleration)

Time = 10 seconds

To find the final velocity, we would use the first equation of motion;

[tex] V = U + at[/tex]

Where;

V is the final velocity.

U is the initial velocity.

a is the acceleration.

t is the time measured in seconds.

Substituting into the formula, we have;

[tex] V = 30 + (-5)*10[/tex]

[tex] V = 30 - 50[/tex]

Final velocity, V = -20 m/s

CHEGG A neutron star has a mass of 2.08 × 1030 kg (about the mass of our sun) and a radius of 6.73 × 103 m. Suppose an object falls from rest near the surface of such a star. How fast would it be moving after it had fallen a distance of 0.0093 m? (Assume that the gravitational force is constant over the distance of the fall, and that the star is not rotating.

Answers

Let g be the acceleration due to gravity on the surface of the star. By Newton's second law, the gravitational force felt by the object has a magnitude of

F = GMm/r ² = mg

where

• G = 6.67 × 10⁻¹¹ Nm²/kg² is the gravitational constant,

• M = 2.08 × 10³⁰ kg is the mass of the star,

• m is the unknown mass of the object, and

• r = 6.73 × 10³ m is the radius of the star

Solving for g gives

g = GM/r ²

g = (6.67 × 10⁻¹¹ Nm²/kg²) (2.08 × 10³⁰ kg) / (6.73 × 10³ m)²

g ≈ 3.06 × 10¹² m/s²

The object is in free fall with uniform acceleration and starting from rest, so its speed after falling 0.0093 m is v such that

v ² = 2g (0.0093 m)

v = √(2g (0.0093 m))

v ≈ 240,000 m/s ≈ 240 km/s

Normal conversation has a sound level of about 60 dB. How many times more intense must a 10,000-Hz sound be compared to a 1000-Hz sound to be perceived as equal to 60 phons of loudness

Answers

Answer: A 10,000-Hz sound is 10 times more intense as compared to a 1000-Hz sound to be perceived as equal to 60 phons of loudness.

Explanation:

The formula used is as follows.

[tex]\beta = 10 dB log (\frac{I}{I_{o}})\\60 = 10 dB log (\frac{I}{I_{o}})[/tex]

[tex]I_{o} = 10^{-12}[/tex] normal threshold

The difference is sound level is as follows.

60 - 60 = 0

Hence,

[tex]0 = 10 dB [log (\frac{I_{f}}{I_{o}}) - log (\frac{I_{i}}{I_{o}})]\\log (\frac{1000}{I_{o}}) = log (\frac{10000 x}{I_{o}})\\log (10^{15}) = log (10^{16}x)\\15 = 16 + log x\\log x = 1\\x = 10[/tex]

This means that 10,000 Hz sound is 10 times more intense.

Thus, we can conclude that a 10,000-Hz sound is 10 times more intense as compared to a 1000-Hz sound to be perceived as equal to 60 phons of loudness.

A local FM radio station broadcasts at a frequency of 100.8 MHz. Calculate the energy of the frequency at which it is broadcasting. Energy

Answers

Answer:

[tex]E=6.68\times 10^{-26}\ J[/tex]

Explanation:

Given that,

The frequency of FM ratio station, f = 100.8 MHz = 100.8 × 10⁶ Hz

We need to find the energy of the wave. We know that,

Energy, E = hf

Put all the values,

[tex]E=6.63\times 10^{-34}\times 100.8\times 10^6\\\\=6.68\times 10^{-26}\ J[/tex]

So, the energy of the wave is equal to [tex]6.68\times 10^{-26}\ J[/tex].

On Ramesh’s13th birthday, his father invited all his friends and their relatives. It was a big party with lots of food and DJs. Ramesh didn’t like the loud sound of DJs and asked his father to play it in a low volume so that their neighbours do not get much disturbed and people at the party can also enjoy the music. Ramesh’s father felt good for his wisdom and did as he said.

→Do you think when loud music is played at a party is acceptable to all the people living in, neighbourhood? Give a reason for your answer
→How can you control noise pollution at your end?

Answers

I go inside and take a nap normally that will help maybe play music

You use a force sensor to measure the weight of an object 10 times, and get the following values: 2.8, 2.6, 2.9, 3.1, 2.4, 2.9, 3.2, 2.5, 2.7, 3.0, where all ten values are in units of N. What is the mean weight of the object, as well as the measurement uncertainty of the weight?

Answers

Answer: Mean weight = 2.81 N and  Measurement of uncertainty = 0.82 N

Explanation:

Mean =  [tex]\dfrac{\text{Sum of observations}}{\text{number of observations}}[/tex]

Mean weight is [tex]($\mu)=\frac{2.8+2.6+2.9+3.1+2.4+2.9+3.2+2.5+2.7+3.0}{10}[/tex]

[tex]=2.81$[/tex]

[tex]$\sum_{i=1}^{10}\left(x_{i}-\mu\right)^{2}=0.61[/tex]

[tex]$\sigma=\sqrt{\frac{1}{N-1} \sum_{i=1}^{10}\left(x_{i}-\mu\right)^{2}}[/tex]

[tex]=\sqrt{\frac{1}{10-1} 0.61}=0.082$[/tex]

Measurement of uncertainty will be  [tex]$\sigma=0.082$[/tex]  

hence,  Weight [tex]$W=2.81 \pm 0.082 N$[/tex]

A person places a cup of coffee on the roof of his car while he dashes back into the house for a forgotten item. When he returns to the car, he hops in and takes off with the coffee cup still on the roof.
(a) If the coefficient of static friction between the coffee cup and the roof of the car is 0.24, what is the maximum acceleration the car can have without causing the cup to slide?
(b) What is the smallest amount of time in which the person canaccelerate the car from rest to 13 m/s andstill keep the coffee cup on the roof?

Answers

Answer:

(a) The acceleration is 2.35 m/s^2.

(b) The time is 5.53 s.

Explanation:

coefficient of friction = 0.24

(a) The acceleration of the car is

[tex]a =\mu g\\\\a = 0.24 \times9.8\\\\a = 2.35 m/s^2[/tex]

(b) initial velocity, u =0, final velocity, v = 13 m/s

Let the time is t.

Use first equation of motion

v = u + a t

13 = 0 + 2.35 x t

t = 5.53 seconds

Which of the following refers to a force acting toward the center of a circular
motion?
A. Centrifugal force
B. Circular force
C. Central force
D. Centripetal force

Answers

Answer:

D. Centripetal Force :)

A hot air balloon is moving at a speed of 10 meters/second in the +x direction. The balloonist throws a brass ball with a velocity of -2
meters/second with respect to himself. If the ball lands after 20 seconds, about how far does it land horizontally from the point at which it was
released?
OA 98 meters
OB. 160 meters
OC. 196 meters
OD. 420 meters

Answers

Answer:

160 meters

Relative of speed Vr = 10 -2 = 8 m/s    (horizontal speed)

20 sec * 8 m/s = 160 m      since ball travels 20 sec

Answer:

160 meters

Explanation:

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Objects that arethree-dimensional I need help please help me. Mr. Jackson orders a lunch special. The cost of each lunch is $6.00. The delivery man charges $2.00 for delivery. Complete the table below and write an expression to determine "Cost of ordering "AND" lunches. Does the table show a direct proportional relationship? If so, what is the constant of proportionality? What is 1/3 of 30% of 5/6 of 0.6 of 12? solve the equation 3x2x=5 What is the "best" explanation for why the universe is the way it is?A) god created the universeB) there is a multiverse and this one happens to be perfect for life.C) this is the only universe and it happens to be perfect for life.D) It is all in illusion and none of it exists.E) none of the above, they are all just guesses.I know the answer I just wanna see what you guys think.i will give brainly if you get it right. Who was the first president of the United States of America? The characteristics of broadcast media Question 7 of 10 Which transition word best connects the ideas within the following paragraph? Some people who disagree with the idea of climate change may refer it as a "non-science." these people may not realize that this claim is based on non-science. A. Now B. Then O C. However D. Therefore Which one of the following is an example of dramatic cultural adaptation that impactsglobalization on cultural diversity?A. For an area that is hot and humid, people move to a colder climate.B. For an area that lacks fertile farmland, food is imported.C. For an area that is often windy and cold the common practice is to wear hats,D. For an area that is snowy people move to a warmer climate, andrea is planning a birthday party and wants to include a cheese board with the desserts.she reads online that she should have 110g of cheese per person ,but the cheese is sold in blocks of 500gHow many blocks of cheese should she buy to ensure that each guest can have 110g of cheese? Helppppppppppppppppppppppppppppppppppppppppppp meeeeee Which mediums can be used to communicate a message? Select three options.dramapaintingsoundstastestext How is plate tectonics involved in ocean expansion? A. Describe four types of information that you can enter into a worksheet cell when using a spreadsheet package, giving specific examples. Is a method for reading American poetry a strong or weak topic What words or phrases show ethos Condense the expression into asingle logarithm and simplify.2log10x + + log105 explain mass in physics