What is the sign of heat(Q), Work(W), or Temperature for these following situations. Say if it's +,-, or 0.
1)You hit a nail with a hammer: +W, Q=0, T=0
2)You hold a nail over a Bunsen burner: Q=+Q, Temp:constant, W=0
3)You compress the air in a bicycle pump by pushing down on the handle very rapidly: -W, Temp:-, Q is -.
4)You turn on a flame under a cylinder of gas, and the gas undergoes an isothermal expansion:
isothermal is constant T, +Q, W is +
5)A flame turns liquid water into steam:
+Q,+W,+T
6)High pressure steam spins a turbine:
T inc so +, +Q, +W
7)Steam contacts a cold surface and condenses:
-Q, -W, Temp decreases
Can you check my work and correct me?
2. does the temp of the nail not increase?
3. When you squeeze gas it gets hot. If you do it rapidly enough there is no time for heat to escape.
4. That did the gas do work on?
5. Again I do not see any work being done.
6. The steam expands through the turbine, losing temperature and doing work
7. Again what work is being done?
You have to define what the system is. In case of 1) if I take the system to be the nail, then
W = 0
Q = positive
T = Positive.
By definition, work is the change in itnernal energy due to a change in the external parameters of a system. In case of the nail, the external parameters (like volume) do not change. What happens is that work is performed by the person hammering the nail, but this converted to heat via friction and this heat is delivered to the nail.
The first law for the nail is:
Delta U = Q - W
I.e. internal energy gain of the nail is heat delivered to the nail minus work perfomed by the nail. The latter is zero and the former is positive, so the nail gains in internal energy, which causes the temperature to rise.
Your answers for the sign of work (W) and temperature (T) are correct. However, there are a few incorrect answers for the sign of heat (Q). Here are the corrections:
1) You hit a nail with a hammer: Q=0, W=0, T=0 (Correct)
2) You hold a nail over a Bunsen burner: Q=+Q, W=0, Temp: constant (Incorrect)
Correction: Q=+Q, W=0, T=+T (Temperature increases)
3) You compress the air in a bicycle pump by pushing down on the handle very rapidly: Q=-Q, W=0, T=-T (Correct)
4) You turn on a flame under a cylinder of gas, and the gas undergoes an isothermal expansion: Q=+Q, W=+W, T=0 (Correct)
5) A flame turns liquid water into steam: Q=+Q, W=+W, T=+T (Correct)
6) High-pressure steam spins a turbine: Q=+Q, W=+W, T=+T (Correct)
7) Steam contacts a cold surface and condenses: Q=-Q, W=-W, T=-T (Correct)
Overall, you did a good job, but there were a few minor mistakes. Keep up the good work!
Your answers are mostly correct, but there are a couple of corrections to be made:
1) You hit a nail with a hammer: Work (W) should be negative (-W) since you are applying a force against the direction of motion of the nail, which means work is done on the nail. Heat (Q) and temperature (T) would be zero (0) in this case.
2) You hold a nail over a Bunsen burner: Heat (Q) should be positive (+Q) as the nail is absorbing heat from the burner. Work (W) would be zero (0) in this case, as there is no mechanical work being done on or by the nail. The temperature (T) would remain constant, as long as the system is isolated.
3) You compress the air in a bicycle pump by pushing down on the handle very rapidly: Work (W) should be negative (-W) since you are applying a force to compress the air, meaning work is done on the air. The temperature (T) would increase, so it should be represented as a positive (+T). Heat (Q) is negative (-Q) since some of the energy of the system is lost as heat due to compression.
4) You turn on a flame under a cylinder of gas, and the gas undergoes an isothermal expansion: Work (W) should be positive (+W) as the gas is expanding against an external pressure, and work is being done by the gas. Heat (Q) is also positive (+Q) as heat is being transferred to the gas to maintain constant temperature. The temperature (T) remains constant, so it should be represented as zero (0) in this case.
5) A flame turns liquid water into steam: You are correct with this answer. Heat (Q), work (W), and temperature (T) would all be positive (+Q, +W, +T) as heat is transferred to the water causing it to boil, work is done by the expanding steam, and temperature increases.
6) High-pressure steam spins a turbine: Heat (Q), work (W), and temperature (T) would all be positive (+Q, +W, +T) as high-pressure steam transfers heat to the turbine, work is done by the steam on the turbine blades, and temperature increases.
7) Steam contacts a cold surface and condenses: Heat (Q) would be negative (-Q) as steam loses heat and undergoes a change of phase to condense. Work (W) would be negative (-W) if the steam does work on the surface, but it may not always be significant. The temperature (T) would decrease as a result of condensation, so it should be represented as a negative change (-T) or a decrease.
Overall, your understanding is good, and just a few adjustments were needed.