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2 years ago

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Your teacher burns a piece of steel wool in class, demonstrating the chemical property, flammability. You are curious to see wha

t other things can demonstrate chemical properties. Which of these does not demonstrate a chemical change?

1 answer:

LekaFEV [45]2 years ago

3 0

Answer:

I assume by "which" of these you're looking for an example. Water freezing into ice or water, or evaporation, the process of turning from liquid into vapor, would not be chemical changes.

Explanation:

These are physical changes because they do not form a new substance, a chemical change requires a change in the chemical makeup of the substance.

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Lauren wants to know which location in her apartment is best for growing African violets. She has three African violets. She put

Harrizon [31]

First, before determining which variable is which, we go over the definition of each.
The independent variable is the one which is intentionally changed in order to investigate its effect on the dependent variable.
The dependent variable is monitored and changes occur in it due to the changing conditions of the independent variable.

In this case, the location of the African violets is the independent variable as it is intentionally changed, while the rate of growth of the African violets is the dependent variable as it is being measured.

5 0

1 year ago

What is Yusef most likely finding?

Ratling [72]

Explanation:

yusef adds all of the values in his data set and then divide by the number of values in the set. the actual density of iron is 7.874 g/ml .

4 0

1 year ago

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

1 year ago

A ledge on a building is 18 m above the ground. A taut rope attached to a 4.0-kg can of paint sitting on the ledge passes up ove

True [87]

Answer:t=5.07 s

Explanation:

Given

height of Building h=18 m

mass of Paint can $m_1=4 kg$

mass of second can $m_2=3 kg$

let T be the Tension in the rope

For 4 kg can

$4g-T=4a$

$T=4(g-a)$ ----1

For 3 kg can

$T-3g=3a$

$T=3(g+a)$ ----2

From 1 and 2

$4(g-a)=3(g+a)$

$g=7a$

$a=\frac{g}{7}$

So time taken to cover 18 m is

$h=ut+\frac{at^2}{2}$

$18=0+\frac{g\cdot t^2}{7\times 2}$

$t^2=\frac{18\times 2\times 7}{g}$

$t=5.07 s$

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1 year ago

What is the weight of an astronaut with a mass of 75 kg on the moon? The gravitational field strength on the moon is 1.6 Nkg-1.

bearhunter [10]

okay this is kinda easy

<u>What is the gravitational field strength on the moon?</u>

The Moon has a gravitational field strength of 1.6 N/kg.

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1 year ago