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3 years ago

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In which of these situations is convection most likely the main form of heat transfer? A.Warm air from a heater on the first flo

or of a house moves to the upper floors. B.The sides of a metal pan become hot when the pan is placed on a stove burner. C.A person gets a sunburn from lying on the beach too long.
D.An ice cube melts when a person holds it in his hand.

2 answers:

Kitty [74]3 years ago

3 0

The answer is D.An ice cube melts when a person holds it in his hand
The heat from your body is causing the ice cube to melt

12345 [234]3 years ago

3 0

Answer:

the correct Answer is A.

Explanation:

i just took the test

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cual seria el consumo semanal de un refrigerador que esta encendido 12 horas diarias con una potencia de 0.8kw

aniked [119]

Answer:

jajajaja sorry no ablaru inglich jajj yes or nou?

4 0

3 years ago

A coil with an inductance of 2.8 H and a resistance of 12 Ω is suddenly connected to an ideal battery with ε = 89 V. At 0.086 s

Thepotemich [5.8K]

Answer:

The stored energy is 140.7 watt.

The thermal energy is 62.7 watt.

The delivered energy is 203.4 watt.

Explanation:

Given that,

Inductance = 2.8 H

Resistance = 12 Ω

Potential $\epsilon_{0}=89\ V$

Time = 0.086 s

(a). We need to calculate the energy stored in the magnetic field

Using formula of current

$i=i_{max}(1-e^(\frac{-t}{\tau}))$

Using formula of energy

$U=\dfrac{1}{2}Li^2$

On differentiating

$\dfrac{dU}{dt}=Li\frac{di}{dt}$

$\dfrac{dU}{dt}=L\dfrac{d}{dt}(i_{max}(1-e^(\frac{-t}{\tau}))$

Again differentiating

$\dfrac{dU}{dt}=\dfrac{\epsilon^2}{R}(1-e^{\frac{-t}{\tau}})e^{\frac{-t}{\tau}}$

$\dfrac{dU}{dt}=\dfrac{\epsilon^2}{R}(1-e^{\frac{-\t\times R}{L}})e^{\frac{-t\times R}{L}}$

Put the value into the formula

$\dfrac{dU}{dt}=\dfrac{(89)^2}{12}(1-e^{\dfrac{-0.086\times12}{2.8}})e^{\dfrac{-0.086\times12}{2.8}}$

$\dfrac{dU}{dt}=140.7\ watt$

(b). We need to calculate the thermal energy

Using formula of thermal energy

$P=i^2R$

$P=\dfrac{\epsilon^2}{R}(1-e^{\frac{-t}{\tau}})^2$

Put the value into the formula

$P=\dfrac{89^2}{12}(1-e^{\dfrac{-0.086\times12}{2.8}})^2$

$P=62.7\ Watt$

(c). We need to calculate the delivered energy by the battery

Using formula of energy

$P'=P+\dfrac{dU}{dt}$

$P'=62.7+140.7$

$P'=203.4\ watt$

Hence, The stored energy is 140.7 watt.

The thermal energy is 62.7 watt.

The delivered energy is 203.4 watt.

5 0

4 years ago

A force of 50 N ,at an angle of 20°,was applied while pulling a 30 kg sled horizontally across the snow. If 939.69 J of work was

artcher [175]

Answer:

20m

Explanation:

w = f × d

= (50cos20) × d

therefore, d = 20m

6 0

3 years ago

There is a close relationship between magnetic forces and the generation of electric current. Explain how magnets can be used to

Snowcat [4.5K]

Inside a generator is a magnet, some electrical wire, and a source of mechanical energy. The mechanical energy moves the wire into the magnetic field of the magnet so that the wire cuts through the magnetic lines of force. As a result, electric current is produced. Electric generators can come in all sizes

3 0

3 years ago

a 1150 kg car is on a 8.70 hill. using x-y axis tilted down the plane, what is the x-component of the normal force(unit=N)

rodikova [14]

The x-component of the normal force is equal to <u>1706.45 N.</u>

Why?

To solve the problem, and since there is no additional information, we can safely assume that the x-axis is parallalel to the hill surface and the y-axis is perpendicular to the x-axis. Knowing that, we can calculate the components of the normal force (or weight for this case), using the following formulas:

$N_{x}=W*Sin(\alpha)=mg*Sin(\alpha)\\\\N_{y}=W*Cos(\alpha)=mg*Cos(\alpha)$

Now, using the given information, we have:

$mass=m=1150Kg\\\alpha=8.70\°\\g=9.81\frac{m}{s^{2}}$

Calculating, we have:

$N_{x}=mg*Sin(\alpha)$

$N_{x}=1150Kg*9.81\frac{m}{s^{2}}*Sin(8.70\°)\\\\N_{x}=11281.5\frac{Kg.m}{s^{2} }*Sin(8.70\°)=1706.45\frac{Kg.m}{s^{2} }=1706.45.23N$

Hence, we have that the x-component of the normal force is equal to <u>1706.45 N.</u>

Have a nice day!

3 0

4 years ago