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Mazyrski [523]
3 years ago
5

why is it incorrect to think that the more digits you include in your answer , the more accurate it is ?

Physics
1 answer:
Anestetic [448]3 years ago
8 0
Because the more that u answer with the extra digits the more u make ur answer wrong?
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Air at 3 104 kg/s and 27 C enters a rectangular duct that is 1m long and 4mm 16 mm on a side. A uniform heat flux of 600 W/m2 is
ad-work [718]

Answer:

T_{out}=27.0000077 ºC

Explanation:

First, let's write the energy balance over the duct:

H_{out}=H_{in}+Q

It says that the energy that goes out from the duct (which is in enthalpy of the mass flow) must be equals to the energy that enters in the same way plus the heat that is added to the air. Decompose the enthalpies to the mass flow and specific enthalpies:

m*h_{out}=m*h_{in}+Q\\m*(h_{out}-h_{in})=Q

The enthalpy change can be calculated as Cp multiplied by the difference of temperature because it is supposed that the pressure drop is not significant.

m*Cp(T_{out}-T_{in})=Q

So, let's isolate T_{out}:

T_{out}-T_{in}=\frac{Q}{m*Cp}\\T_{out}=T_{in}+\frac{Q}{m*Cp}

The Cp of the air at 27ºC is 1007\frac{J}{kgK} (Taken from Keenan, Chao, Keyes, “Gas Tables”, Wiley, 1985.); and the only two unknown are T_{out} and Q.

Q can be found knowing that the heat flux is 600W/m2, which is a rate of heat to transfer area; so if we know the transfer area, we could know the heat added.

The heat transfer area is the inner surface area of the duct, which can be found as the perimeter of the cross section multiplied by the length of the duct:

Perimeter:

P=2*H+2*A=2*0.004m+2*0.016m=0.04m

Surface area:

A=P*L=0.04m*1m=0.04m^2

Then, the heat Q is:

600\frac{W}{m^2} *0.04m^2=24W

Finally, find the exit temperature:

T_{out}=T_{in}+\frac{Q}{m*Cp}\\T_{out}=27+\frac{24W}{3104\frac{kg}{s} *1007\frac{J}{kgK} }\\T_{out}=27.0000077

T_{out}=27.0000077 ºC

The temperature change so little because:

  • The mass flow is so big compared to the heat flux.
  • The transfer area is so little, a bigger length would be required.
3 0
3 years ago
A person travels by car from one city to an-
Mademuasel [1]
<h2>Answer:</h2>

<h2>Explanation:</h2>

First, let's refer to the distance formula:

d=v*t, where d is distance, v is velocity or speed and t is time.

Now, let's find the distance covered by each individual speed that the car had:

<h3>1. Speed 1.</h3>

In order to use the formula, we need to convert minutes into hours since the speed is given in km/h.

21.1 min/60= 0.35 h.

Now, apply the distance formula.

d=(0.35h)*(86.8km/h)= 30.38 km.

<h3>2. Speed 2.</h3>

Convert minutes to hours again and do the same calculations.

10.6min/60=0.18h

d=(0.18h)*(106km/h)= 19.08 km.

<h3>3. Speed 3.</h3>

36.5min/60= 0.61h

d=(0.61h)*(30.9km/h)= 18.85 km.

<h3>4. Obtain the total distance.</h3>

The total distance must be given by the addition of all individual distances traveled by the car on each speed:

Total distance= 30.38 km + 19.08 km + 18.85 km= 68.31 km.

5 0
2 years ago
Define cyber law and its types.​
butalik [34]

Answer:

Cyber Law is a generic term referring to all the legal and regulatory aspects of the internet. Everything concerned with or related to or emanating from any legal aspects or concerning any activities of the citizens in the cyberspace comes within the ambit of cyber laws.

<h2>Types :-</h2>
  • Copyright
  • Patents
  • Trademarks or Service Marks
  • Trade Secrets
  • Domain Disputes
  • Contracts
  • Privacy
  • Employment
  • Defamation

Explanation:

<h2>HOPE IT HELPS YOU!! </h2>
5 0
3 years ago
A crate is being lifted into a truck. If it is moved with a 2470 N force and 4850 J of work is done, then how far is the crate b
olchik [2.2K]

Answer:1.96m

Explanation:

Work=4850J

Force=2470N

Distance =work ➗ force

Distance =4850 ➗ 2470

Distance =1.96m

7 0
3 years ago
Which best distinguishes between the inner and outer planets?
Murrr4er [49]
Either a or b 
not exactly sure which
3 0
4 years ago
Read 2 more answers
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