Determine each of the following quantities (a) W, (b) delta U, (c) Q. Include algebraic sign.?

In moving out of a dormitory at the end of the semester, a student does 2.77 x 10^4 J of work. In the process, his internal energy decreases by 4.94 x 10^4 J.

Determine each of the following quantities (a) W, (b) delta U, (c) Q. Include algebraic sign.?
Hi Tamara H





Your question is about the first law of thermodynamics, which can be written (mathematically) as:





dU = dQ - W





Where dU is the change in internal energy of the system, dQ is the heat added to the system and W is the work the system does on its surroundings.





In this case the system is the student. The work done by the student, W, is given as 27.7kJ. The change in internal energy of the student is dU, given as -49.4kJ. This value is negative, since the energy decreases. Now we can solve for dQ:





dU = dQ - W





-49400 = dQ - 27700





dQ = -21.7kJ. The negative value means the heat is lost from the student to his surroundings. Let's do a sanity check: our results tell us that the student has lost an amount of internal energy (-49.4kJ), some of which has done some work (27.7kJ) and some of which was lost to heat (21.7kJ). This makes sense, so our results are reasonable.





Summary:


dU = -4.94*10^4J


Q = -2.17*10^4J


W = 2.77*10^4J








Hope this helps!


The Chicken