A60-kg skier starts from rest from the top of a 50-m high slope. if the work done by friction is -6.0 kj, what is the speed of the skier on reaching the bottom of the slope?

At the top of the hill, the skier has only potential energy, because its speed is zero (he starts from rest), so his mechanical energy is


During his descent, the work done by the friction is . This means that the skier loses 6000 J of energy during his descent, so its final mechanical energy at the bottom is


At the bottom of the hill, the mechanical energy is only kinetic energy K, because now the altitude of the skier is zero: h=0, so the potential energy is zero (U=0). So,

And so, from this we find the speed of the skier at the bottom of the hill:

No because scientist are still changing there mines today so they are not correct to this day