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Degger [83]
3 years ago
5

A cup of hot coffee can be cooled by placing a cold spoon in it. A spoon of which of the following materials would be most effec

tive for this purpose: aluminum, copper, iron, or glass? Assume all spoons have the same mass.
Physics
1 answer:
arsen [322]3 years ago
8 0

Answer: copper

Explanation: when a spoon is placed in a hot coffee, the coffee will cool off based on the concept of heat transfer.

The coffee is at a higher temperature compared to the spoon, hence there is conduction of heat by the spoon from the coffee.

Heat is now transfered from the coffee to the spoon, the rate of heat transfer ( for this case coffee to spoon) is dependent on some properties but for this case, the thermal conductivity is of the most important.

A material of high thermal conductivity have a very fast rate of heat transfer and a material of low thermal conductivity have a slow rate of heat transfer.

Below is the value of thermal conductivity for copper, aluminum, iron and glass.

Copper (385 w/m.K)

Aluminum (205 W/m.K)

Iron (79.5 W/m.K)

Glass (0.8 W/m.K)

It can been seen that copper has the highest value for thermal conductivity which implies that it will conduct heat faster compared to others thus cooling the coffee faster.

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Answer: The copper wiring most likely caused the mini-refrigerator fire.

Explanation: A mini-refrigerator may have one or more evaporator fan motors. These motors have copper wiring. In some situation these copper wires gets overheated. It may result to the firing of the mini-refrigerator.

Therefore, the mini-refrigerator fire was most likely caused by copper wiring.

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Answer:

W = 46 J

Explanation:

We need to find the angle between the two vectors Force vector and displacement vector.

First we will find the angle α of the force vector

tan\alpha =\frac{1}{8} \\\\\\alpha =7.125 deg\\

Then we find the angle β of the displacement vector

tan\beta=\frac{2}{6} \\\\beta = 18.43 deg\\

With these two angles we can find the angle between the two vectors

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The definition of work is given by the expression

W=F*d*cos (theta)

The absolute value of F will be:

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The absolute value of d will be:

d=\sqrt{(6 )^{2}+(2)^{2}  } \\d= 6.32m\\

Now we have:

W=8.06*6.32*cos(25.56)\\W=46 J

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