A hoop with mass m and radius R is rolling without slipping on a horizontal surface with its center moving at a speed v. The rotational inertia of the hoop about its center is mR2. What is its total kinetic energy

Apassenger walks toward the rear of a moving train. describe her motion as seen from a reference point on the train. then describe it from a reference point on the ground

Could someone me find the answer to this problem.

Electromagnetic induction. a coil of wire contains n turns and has an electrical resistance r. the radius of each turn is a. initially, inside the coil there exists a uniform magnetic field of magnitude b0 parallel to the axis of the coil. the magnetic field is then reduced slowly. the current induced in the coil is i. how long does it take for the magnitude of the uniform field to drop to zero?