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natta225 [31]
3 years ago
5

engineers who design battery operated devices suck as sell phones and MP3 players try to make them as efficient as possible. An

engineer test a cell phone and finds that the batteries supply 10,000 J of energy to make 5,500 J of output energy in the form of sound and light for the screen. How efficient is the phone
Physics
1 answer:
ICE Princess25 [194]3 years ago
8 0
If the 5,500 J of sound and light is the ONLY useful output
from the phone, then the phone's efficiency is

                   (5,500J / 10,000J)  =  0.55  =  55% .

But the test engineer forgot one little minor almost insignificant detail.
As a test engineer myself, I'd say that he needs to turn in his laptop
and soldering iron, and think about changing his career to a job for
which he may be better suited, like 8 hours a day in a highway toll-booth.  

What about that little radio transmitter and receiver inside the phone,
that maintain digital RF communication with the nearest cell tower ?
Without that microscopic radio transceiver ... plus 30 or 40 apps
that are always running unless you shut them off ... the device in your
pocket is essentially a flat rock with one side that sometimes glows.
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. A PNP transistor is connected in a circuit so that the collector-base junction remains reverse biased and the emitter-base jun
Elodia [21]

Explanation :

A power amplifier is used to amplify electric signals i.e. to increase the low power signal to higher powers.

A PNP transistor is connected in a circuit so that the collector-base junction remains reverse biased and the emitter-base junction is forward biased.

This transistor can be used as a power amplifier because it gives a much larger output current. The gain of an amplifier shows the amount of amplification. It is the difference between the input and the output signals.

6 0
3 years ago
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Calculate the number of electrons in a small, electrically neutral silver pin that has a mass of 7.1 g. Silver has 47 electrons
Assoli18 [71]

<u>Answer:</u> The number of electrons in given amount of silver are 1.87\times 10^{24}

<u>Explanation:</u>

To calculate the number of moles, we use the equation:

\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}

We are given:

Given mass of silver = 7.1 g

Molar mass of silver = 107.87 g/mol

Putting values in above equation, we get:

\text{Moles of silver}=\frac{7.1g}{107.87g/mol}=0.066mol

Number of electrons in 1 atom of silver = 47

According to mole concept:

1 mole of an element contains 6.022\times 10^{23} number of particles

So, 0.066 moles of silver will contain = -(0.066\times 47\times 6.022\times 10^{23})=1.87\times 10^{24} number of electrons

Hence, the number of electrons in given amount of silver are 1.87\times 10^{24}

7 0
3 years ago
A ball traveling at 15 m/s hits a bat with a force of 200N. How much force does the bat (moving at 20m/s)
just olya [345]

Answer:

200 N

Explanation:

Given that,

A ball traveling at 15 m/s hits a bat with a force of 200 N.

We need to find the force that the bat moving at 20 m/s hit the ball with.

We know that, this probelm is based on Newton's third law of motion. The force that the ball exerting on bat should be equal to the force that the bat exerting in the ball but in opposite direction.

It would mean that the ball hits the ball with a force of 200 N. Hence, the correct option is (a).

8 0
3 years ago
Sayid made a chart listing data of two colliding objects. A 5-column table titled Collision: Two Objects Stick Together with 2 r
Alborosie

Answer:

6 m/s is the missing final velocity

Explanation:

From the data table we extract that there were two objects (X and Y) that underwent an inelastic collision, moving together after the collision as a new object with mass equal the addition of the two original masses, and a new velocity which is the unknown in the problem).

Object X had a mass of 300 kg, while object Y had a mass of 100 kg.

Object's X initial velocity was positive (let's imagine it on a horizontal axis pointing to the right) of 10 m/s. Object Y had a negative velocity (imagine it as pointing to the left on the horizontal axis) of -6 m/s.

We can solve for the unknown, using conservation of momentum in the collision: Initial total momentum = Final total momentum (where momentum is defined as the product of the mass of the object times its velocity.

In numbers, and calling P_{xi} the initial momentum of object X and P_{yi} the initial momentum of object Y, we can derive the total initial momentum of the system: P_{total}_i=P_{xi}+P_{yi}= 300*10 \frac{kg*m}{s} -100*6\frac{kg*m}{s} =\\=(3000-600 )\frac{kg*m}{s} =2400 \frac{kg*m}{s}

Since in the collision there is conservation of the total momentum, this initial quantity should equal the quantity for the final mometum of the stack together system (that has a total mass of 400 kg):

Final momentum of the system: M * v_f=400kg * v_f

We then set the equality of the momenta (total initial equals final) and proceed to solve the equation for the unknown(final velocity of the system):

2400 \frac{kg*m}{s} =400kg*v_f\\\frac{2400}{400} \frac{m}{s} =v_f\\v_f=6 \frac{m}{s}

7 0
3 years ago
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Why does the speed of an object change when a force acts on it?
Crazy boy [7]
It changes because force is somewhat like pressure. Force is continuously against the object so as a result, speed changes .
7 0
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