High School Physics Competition: Change in Entropy

AI Thread Summary
In a physics competition, a question regarding the change in entropy when 1.25 x 10^3 J of heat is added to a system at a constant temperature of 75.0°C was discussed. The calculated change in entropy was found to be approximately 3.59 J/K. Confusion arose between two answer choices, with one option labeled with a hashtag, which was clarified to indicate a negative value. Ultimately, it was confirmed that the change in entropy is positive, making the correct answer +3.59 J/K. The hashtag was identified as a potential misprint, leading to the conclusion that answer c) is the correct choice.
ReneG
Messages
4
Reaction score
1
During a physics competition, I came across this question.
What is the change in entropy of the system when 1.25 " 103 J of heat is added to the system that is maintained at a constant 75.0 C?

My work was
\begin{align*}\Delta S &= \frac{Q}{T} \\ \Delta S &= \frac{1.25 \times 10^3 \, \mathrm{J}}{348 \, \mathrm{K}} \\ \Delta S &= 3.59 \,\,\mathrm{\left( J/K\right )} \end{align*}

but I was stuck in between two answer choices

c) + 3.59 J/K
d) # 3.59 J/K

I had no idea what the hashtag meant, so I skipped it. Can someone clear this up for me?
 
Physics news on Phys.org
Honestly I have no idea, but certainly the change in entropy is positive, so answer c) is correct. Maybe it's a misprint?
 
I guess what dipole said it's right 'cause it sometimes happens
 
Last edited:
For anyone who was wondering, the hashtag just meant "negative". Thank you dipole.
 
Thread 'Variable mass system : water sprayed into a moving container'
Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
I was thinking using 2 purple mattress samples, and taping them together, I do want other ideas though, the main guidelines are; Must have a volume LESS than 1600 cubic centimeters, and CAN'T exceed 25 cm in ANY direction. Must be LESS than 1 kg. NO parachutes. NO glue or Tape can touch the egg. MUST be able to take egg out in less than 1 minute. Grade A large eggs will be used.
Back
Top