Q: One person says that the potential energy of a particular book kept in a bookshelf is 25 J and the other says it is 35 J. Is one of them necessarily wrong?

A: It is possible that one of them is wrong, but it is also possible that both are correct.

The potential energy of an object depends on its position and the reference point chosen to calculate it. If both individuals are using different reference points to calculate the potential energy of the book, then they may obtain different values.

For example, if one person is using the floor as the reference point and the other person is using the top of the bookshelf as the reference point, then they will obtain different values for the potential energy of the book.

Therefore, it is important to know the reference point being used to calculate the potential energy of the book in order to determine if one person is necessarily wrong or if both values could be correct.