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I am Lyosha [343]

3 years ago

7

Your total calorie _____ is an estimation of how many calories you burn when you exert yourself. A.Moderate B.Conditions C.Expen

diture D.Anaerobic ( Subject P.E )

1 answer:

joja [24]3 years ago

6 0

Answer:

C. Expenditure

Explanation:

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Determine the power that needs to besupplied by the fanifthe desired velocity is 0.05 m3/s and the cross-sectional area is 20 cm

Mariulka [41]

Answer:

A fan with an energy efficiency of 30 % would need 62.5 watts to bring a desired volume flow of 0.05 cubic meters per second through a cross-sectional area of 20 square centimeters.

Explanation:

Complete statement is: <em>Determine the power that needs to besupplied by the fan if the desired velocity is 0.05 cubic meters per second and the cross-sectional area is 20 square centimeters.</em>

From Thermodynamics and Fluid Mechanics we know that fans are devices that work at steady state which accelerate gases (i.e. air) with no changes in pressure. In this case, mechanical rotation energy is transformed into kinetic energy. If we include losses due to mechanical friction, the Principle of Energy Conservation presents the following equation:

$\eta\cdot \dot W = \dot K$

$\dot W = \frac{\dot K}{\eta}$ (Eq. 1)

Where:

$\eta$ - Efficiency of fan, dimensionless.

$\dot W$ - Electric power supplied fan, measured in watts.

$\dot K$ - Rate of change of kinetic energy of air in time, measured in watts.

From definition of kinetic energy, the equation above is now expanded:

$\dot W = \frac{\rho_{a}\cdot \dot V}{2\cdot \eta}\cdot \left(\frac{\dot V}{A_{s}} \right)^{2}$ (Eq. 2)

Where:

$\rho_{a}$ - Density of air, measured in kilograms per cubic meter.

$\dot V$ - Volume flow, measured in cubic meters per second.

$A_{s}$ - Cross-sectional area of fan, measured in square meters.

If we know that $\rho_{a} = 1.20\,\frac{kg}{m^{3}}$ , $\dot V = 0.05\,\frac{m^{3}}{s}$ , $\eta = 0.3$ and $A_{s} = 20\times 10^{-4}\,m^{2}$ , the power needed to be supplied by the fan is:

$\dot K = \left[\frac{\left(1.20\,\frac{kg}{m^{3}} \right)\cdot \left(0.05\,\frac{m^{3}}{s} \right)}{2\cdot (0.3)} \right]\cdot \left(\frac{0.05\,\frac{m^{3}}{s} }{20\times 10^{-4}\,m^{2}} \right)^{2}$

$\dot K = 62.5\,W$

A fan with an energy efficiency of 30 % would need 62.5 watts to bring a desired volume flow of 0.05 cubic meters per second through a cross-sectional area of 20 square centimeters.

5 0

3 years ago

For a given wave IF frequency doubles the wavelength

motikmotik

Answer:

C is halved

Explanation:

The frequency and the wavelength of a wave are related by the equation:

$v=f\lambda$

where

v is the speed of the wave

f is the frequency

$\lambda$ is the wavelength

From the equation above, we see that for a given wave, if the wave is travelling in the same medium (and so, its speed is not changing), then the frequency and the wavelength are inversely proportional to each other.

Therefore, if the frequency doubles, the wavelength will halve in order to keep the speed constant:

$\lambda = \frac{v}{f}\\\lambda' = \frac{v}{f'}=\frac{v}{2f}=\frac{1}{2}(\frac{v}{f})=\frac{\lambda}{2}$

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3 years ago

What is compression

Talja [164]

The answer is B) region of high pressure in a medium caused by a passing wave

Compression is the forcing of the molecules of a medium, be it water, air, or something else, as a wave passes by. This forcing together of the molecules raises the pressure of the medium in the area that the wave passes through.

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Which of the following is NOT accelerating?

ivolga24 [154]

I would say the answer to your question is A Ferris wheel turning at a constant speed. The reasoning behind this answer is the fact that traveling in a constant direction at a constant speed is not accelerating. The Ferris wheel is the only option that fits this description. The last option would be incorrect due to independent causes such as speed limit changes as well as turns and stops on the highway.

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3 years ago

Setler [38]

I think the answer is B.

Hope this helps.

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