A small ring R is attached to one end of a light inextensible string of length 70 cm. A fixed rough vertical wire passes through the ring. The other end of the string is attached to a point A on the wire, vertically above R. A horizontal force of magnitude 5.6 N is applied to the point J of the string 30 cm from A and 40 cm from R. The system is in equilibrium with each of the parts AJ and JR of the string taut and angle AJR equal to 90° (see diagram).

1. Find the tension in the part AJ of the string, and find the tension in the part JR of the string. [5]
2. The ring R has mass 0.2 kg and is in limiting equilibrium, on the point of moving up the wire.
3. Show that the coefficient of friction between R and the wire is 0.341, correct to 3 significant figures. [4]
4. A particle of mass m kg is attached to R and R is now in limiting equilibrium, on the point of moving down the wire.
5. Given that the coefficient of friction is unchanged, find the value of m. [3]