This question tested candidates understanding on the concept of conservation of energy. Majority of the candidates were able to solve this problem.  However, few candidates could not solve  this  question correctly because they lack  the knowledge that at maximum height the potential  energy  P.E is equal to the kinetic energy K.E

The expected answer is:
At max. Ht, P.E  =  initial K.E
              =   ½ mu2
              =   ½  x 0.5 x (25)2
              =   156.25 J

             OR

            V2  =  u2   -  2gh
           At maximum height,  v  =  0
           O  =  252  -  2 x 10h
            h  =  31.25m
            P.E  =  mgh
            =  0.5 x 10 x 31.25
            =  156.25J