What is the change in internal energy if 60 J of heat is released from a system and 30 J of work is done on the system? Use U =
1 answer:
The change in internal energy of the system is +30 J
Explanation:
We can solve this problem by using the first law of thermodynamics, which states that the change in internal energy of a system is given by the equation:
where
is the change in internal energy
Q is the heat absorbed by the system (positive if it is absorbed, negative if it is released)
W is the work done by the system (positive if it is done by the system, negative if it is done by the surroundings on the system)
Therefore, in this problem, we have
(heat released by the system)
(work done on the system)
Therefore, the change in internal energy is
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There are some missing data in the text of the problem. I've found them online:
a) coefficient of friction dry steel piston - steel cilinder: 0.3
b) coefficient of friction with oil in between the surfaces: 0.03
Solution:
a) The force F applied by the person (300 N) must be at least equal to the frictional force, given by:
where
is the coefficient of friction, while N is the normal force. So we have:
since we know that F=300 N and
, we can find N, the magnitude of the normal force:
b) The problem is identical to that of the first part; however, this time the coefficienct of friction is
due to the presence of the oil. Therefore, we have:
a) coefficient of friction dry steel piston - steel cilinder: 0.3
b) coefficient of friction with oil in between the surfaces: 0.03
Solution:
a) The force F applied by the person (300 N) must be at least equal to the frictional force, given by:
where
since we know that F=300 N and
b) The problem is identical to that of the first part; however, this time the coefficienct of friction is