A spacecraft can be regarded as a uniform cylinder, 1 m in diameter and of mass 250 kg. It is spinning about its cylindrical axis with a period of 3 s. (a) What is the angular momentum of this isolated system? [3] (b) A mass of 50 g attached to a long string is slowly let out from the (curved) side of the cylinder, until the period has increased to 10 minutes. Explain why the period increases and calculate the length of the string. [10] (c) As the cylinder's angular velocity decreases, there must be a torque acting on it. Draw a diagram showing clearly how the torque arises. [4] (d) Calculate the initial and final kinetic energies of rotation of the system. [3] (e) An electric motor in the cylinder is now switched on to wind in the string slowly. Explain why it has to do work. Where does the work go? [5]