The most important measure is awhips
(1 cal/g °C) x (4000 g) x (45 - 25)°C = 80000 cal = 80 kcal. So the answer is 80 kcal .
Rubbing both pieces cause each piece to have a negative charge.
When two parts have the same they repel each other, so holding one piece up tot he end of the other piece would push it away.
Because one piece is held in the middle by a string, it would rotate the piece in a circle.
If they held the piece to the other end of the one held by a string it would start to rotate in the opposite direction.
If an atom gains electrons, it develops a negative charge equal to the number of electrons gained.
So the net charge on the copper atom which gained 2 electrons will be -2.