Abook weighs 0.5 kilograms on a book shelf that is 2 meters above the ground. what is the potential energy of the book relative to the ground? (hint: you may use 10 n/kg as the value for gravity)

What occurs during a combustion reaction

Asolid cylinder and a cylindrical shell have the same mass, same radius, and turn on frictionless, horizontal axles. the cylindrical shell has light-weight spokes connecting the shell to the axle. a rope is wrapped around each cylinder and tied to blocks of equal masses that are held the same height above the ground. both blocks are released simultaneously. the ropes do not slip. which block hits the ground first? or is it a tie?

Convection currents are caused by differences in what two things?