Answer:
option B
Explanation:
given,
Q = energy input = 70 J
U = increase in internal energy
W is the work done = 20 J
using first law of thermodynamics
The change in internal energy of a system is equal to the heat added to the system minus the work done.
U = Q - W
U = 70 - 20
U = 50 J
The change in internal energy is equal to 50 J
Hence, the correct answer is option B
