What naturally accurring radioisotope is used as the fuel for a nuclear reactor

The coefficient of friction is a number that represents the resistance to sliding between two in contact with one another.

The gun from the crime scene shows tool marks where the serial numbers are ground off. there are also tool marks on the bullets left behind. what information can the tool marks on the bullets and gun provide about the crime? what type of evidence does this information provide, individual or class?

A90db sound wave strikes an eardrum whose area is 5.0×10^-5m^2. how much energy is absorbed by the eardrum per second