Answer: 85J
Explanation:
From the question, we are informed that when spring was wound, 100J of work was done but 15J escaped to the surrounding as heat.
Therefore, the change in internal energy of the spring will be calculated as:
ΔU = q + w
where, q = -15J
w = 100J
ΔU = -15J + 100J
= 85J
