When will chernobyl stop being radioactive

What property is a characteristic of a substance that can be observed and does not change the identity of the substance

The 5-kg cylinder is initially at rest when it is placed in contact with the wall b and the rotor at a. if the rotor always maintains a constant clockwise angular velocity v = 6 rad> s, determine the initial angular acceleration of the cylinder. the coefficient of kinetic friction at the contacting surfaces b and c is mk = 0.2.

Which planet do you think would be easiest for humans to colonize some day?