1. The problem statement, all variables and given/known data There is a tower and a heavy box in it, which weighs 20.000 kg. This box falls down from 70m and after falling 40m(free fall), she is slowed down by magnets on the surface of the box, which interact after falling 40m with copper plates on the tower, which weigh 2.000kg. Then 2 m high, the velocity of the box is 2,77 m/s. Now the question is: What is the change in temperature for the copper plates? Of course friction is neglected! m1=20.000kg h1=70m h2=2m v=2,77m/s c(Copper)=385 J/(kg*K) m2= 2.000kg 3. The attempt at a solution Now I thought about solving this by using the law of conservation of energy, since the potential energy at the beginning is equal to the potential energy at the end+ the kinetic energy the box has+the heat that is absorbed by the copper plates: [TEX] m1 g h1=1/2 m v²+m2 g h2+ m2 c T[/TEX] But in this case, it would not matter, that the slow down process, does not start until the box has covered these 40m and this information would be redundant. So I think my approach is wrong, but I have no idea, what I am actually doing wrong. Can you help me, please?