Physics. Heat exchange

[pastel osprey]

Physics. Heat exchange. Why is the specific heat of aluminum positive but not negative? I got ≈ -969.2 But the answers say that there will be 969.2. We get the equation Q given = Q obtained. It turned out that Q is given = 6300 but Q obtained = -6.5 * (-969,2) = 6299.8 ≈ 6300. So the left and right sides are equal, then why should the answer be positive and not negatively?

[proven bear]

First: What would a negative heat capacity represent?

Second: Why do you write that Q obtained = -6.5 * [Heat capacity], rather than Q obtained = 6.5 * [Heat capacity]?

Also, why 6.5 instead of 65?

[pastel osprey]

I think it's better I will send a photo of my decision. -6.5 is a mass multiplied by a temperature difference

[proven bear]

Yes, but isn't the temperature difference 65 degrees, not 6.5? It's not relevant in this case if you apply it to both sides, but it's not true in general when trying to figure out the energy involved in temperature loss/gain.

[pastel osprey]

The temperature difference is -65 but then -65 is multiplied by a mass of 0.1 and it turns out -6.5. I did not say that -6.5 is the temperature

[proven bear]

Ah, yes, sorry.

Either way: The temperature difference is -65, but if you're taking signs into account, the actual equality is that Qgiven = - Qobtained

Their modulus is the same, which is what the sign-less formulation is getting at, but what the equation really represents is that there's no variation of energy if you consider the entire system.

The variation of energy (Qgiven+ Qobtained) must be 0.

[pastel osprey]

I did not quite understand this explanation. We have an equation Q given = Q obtained And on the right we got 6300, then why did you write that Q = -Q?

[proven bear]

Qgiven = Qobtained is only true if you don't consider the sign.

If you do, then Qgiven = -Qobtained is correct.

Underlying idea being that the total change in energy is 0, and it can be calculated as the sum of all individual changes of energy.

[pastel osprey]

So I need to write down the minus in this equation to make it right?

[proven bear]

Yeah.

[pastel osprey]

Ok, thanks

[pastel osprey]

Then -969.2 will be a correct answer if I have such an equation, right?

[proven bear]

No, you'll get 969.2, which is the correct answer.

[pastel osprey]

Then what is the difference in the records of equations if I have a positive answer? Then why should I write a minus on the right side of the equation?

[proven bear]

You said you were originally getting a negative result, didn't you?

[pastel osprey]

Yes

[pastel osprey]

But what's next?

[proven bear]

What do you mean?

[ionic topaz]

Or this

[ionic topaz]

U have to make sure Q>0 if u use this way

c >0