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3 years ago

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On a hot summer day, a student turns his fan on when he leaves his room in the morning. When he returns in the evening, will the

room be warmer or cooler than the neighboring rooms? Why? Assume all the doors and windows are kept closed.

1 answer:

Virty [35]3 years ago

5 0

Answer:

When the student returns, it will be hotter

Explanation:

We know that the room is closed, so no air is coming in from outside and no air goes outside as the windows and doors are closed. We know the fan is moving and the fan does not cool the air, it only moves the air. Therefore, this process creates kinetic energy that is converted into heat energy (internal) so that room begins to get warmer.

And we know by the the law of Conservation of Energy, there is no loss in energy

So, the room just gets hotter.

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A rich industrialist was found murdered in his house. The police arrived at the scene at 11:00 PM. The temperature of the corpse

d1i1m1o1n [39]

Answer:

The dude was killed around 6:30PM

Explanation:

Newton's law of cooling states:

$T = T_m + (T_0-T_m)e^{kt}$

where,

$T_0$ = initial temp

$T_m$ = temp of room

$T$ = temp after t hours

$k$ = how fast the temp is changing

$t$ = time (hours)

$T_0 = 31$ because the body was initlally 31ºC when the police found it

$T_m = 22$ because that was the room temp

$T = 30$ because the body temp drop to 30ºC after 1 hour

t = 1 because that's the time it took for the body temp to drop to 30ºC

$k=???$ we don't know k so we must solve for this

rearrange the equation to solve for k

$T = T_m + (T_0-T_m)e^{kt}$

$T - T_m= (T_0-T_m)e^{kt}$

$\frac{T - T_m}{(T_0-T_m)}= e^{kt}$

$ln(\frac{T - T_m}{T_0-T_m})=kt$

$\frac{ln(\frac{T - T_m}{T_0-T_m})}{t}=k$

plug in the numbers to solve for k

$k = \frac{ln(\frac{T - T_m}{T_0-T_m})}{t}$

$k = \frac{ln(\frac{30 - 22}{31-22})}{1}$

$k=ln(\frac{8}{9})$

Now that we know the value for k, we can find the moment the murder occur. A crucial information that the question left out is the temperature of a human body when they're still alive. A living human body is about 37ºC. We can use that as out initial temperature to solve this problem because we can assume that the freshly killed body will be around 37ºC.

$T_0 = 37$ because the body was 37ºC right after being killed

$T_m = 22$ because that was the room temp

$T = 31$ because the body temp when the police found it

$k=ln(\frac{8}{9})$ we solved this earlier

t = ??? we don't know how long it took from the time of the murder to when the police found the body

Rearrange the equation to solve for t

$T = T_m + (T_0-T_m)e^{kt}$

$T - T_m= (T_0-T_m)e^{kt}$

$\frac{T - T_m}{(T_0-T_m)}= e^{kt}$

$ln(\frac{T - T_m}{T_0-T_m})=kt$

$\frac{ln(\frac{T - T_m}{T_0-T_m})}{k}=t$

plug in the values

$t=\frac{ln(\frac{T - T_m}{T_0-T_m})}{k}$

$t=\frac{ln(\frac{31 - 22}{37-22})}{ln(8/9)}$

$t=\frac{ln(3/5)}{ln(8/9)}$

$t=\frac{ln(3/5)}{ln(8/9)}$

t ≈ 4.337 hours from the time the body was killed to when the police found it.

The police found the body at 11:00PM so subtract 4.337 from that.

11 - 4.33 = 6.66 ≈ 6:30PM

7 0

3 years ago

The importance of reading a circuit diagram to interpret a wiring diagram?

Nataly [62]

Answer:

The ability to read electrical schematics is a really useful skill to have. To start developing your schematic reading abilities, it's important to memorize the most common schematic symbols. ... You should also be able to get a rough idea of how the circuit works, just by looking at the schematic.

Explanation:

7 0

3 years ago

NEED HELPASAP what is the moisture content of a board if a test sample that originally weighed 11. 5 oz was found to weigh 10 oz

Viefleur [7K]

Answer:

11.5-10/10= 0.15x100 =15%

Explanation:

3 0

2 years ago

X-Ray Inspection

Softa [21]

The answer is the test is being tested towards the lungs the test is done by scanning your body the tools are called “the x rat visional lock space” and the rubber tool is called a deeldo it’s purple with a pencil looking shape perfect for the body.

5 0

3 years ago

If the total length of a measurement is 10 1/2" what is half of this length?

Aneli [31]

Answer:

13.335 CM (1 ft, 1.335 cm)

I am 80% sure this is the answer, but i am not too keen on math so if i am wrong let me know and i will try my best to fix it!

I hope this helped! Have a good day :]

5 0

2 years ago