1) When a block of mass M is suspended by a long wire of  length L, the length of the wire becomes (L + l). The  elastic potential energy stored in the extended wire is :       (1)   Mgl       (2)   MgL     (3) ½ Mgl         (4) ½ MgL      EXPLANATION : 2) A mass (m) is attached to a thin wire and whirled in a  vertical circle. The wire is most likely to break when: (1) the mass is at the highest point (2) the wire is horizontal (3) the mass is at the lowest point (4) inclined at an angle of 60° from vertical EXPLANATION : 3) Ionized hydrogen atoms and a -particles with same  momenta enters perpendicular to a constant magnetic  field, B. The ratio of their radii of their paths rH : r a will  be : (1) 2 : 1 (2) 1 : 2 (3) 4 : 1 (4) 1 : 4 EXPLANATION : 4) Body A of mass 4m moving with speed u collides with  another body B