A closed system undergoes a process in which the work done by the system is 100 J and the internal energy decreases by 50 J. According to the first law of thermodynamics, what is the amount of heat transferred into or out of the system?  

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SSC JE Mechanical 9 Oct 2023 Shift 2 Official Paper-I
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  1. 150 J
  2. 50 J
  3. -150 J
  4. -50 J

Answer (Detailed Solution Below)

Option 2 : 50 J
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Detailed Solution

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Concept:

The first law of thermodynamics

This law states that the total heat given or taken out of the system will always be equal to the work done and change in the internal energy of the system.

​⇒ Q = W + ΔU

Where Q = heat, W = work done, and ΔU = change in internal energy

Calculation:

Given W = 100 J, and ΔU = -50 J

By the first law of thermodynamics,

​⇒ Q = W + ΔU

​⇒ Q = 100 + (-50)

​⇒ Q = 50 J

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