Answer
a). (2) one,
b). Work done by weight = zero, work done by normal force = zero, work done by frictional force =$62.5J$
Work Step by Step
a). There are three forces acting on the hockey puck - the weight of the puck, the normal force and the frictional force.
The motion of the puck is horizontal. Therefore, there is only 1 force which does non-zero work on the puck which is the frictional force.
So, (2) is the answer.
b). Work done by weight of the puck is zero.
Work done by normal reaction force is zero.
$v^{2}=u^{2}+2aS$
$0=25^{2}-2a100$
$a=3.125m/s^{2}$
$F=ma=0.2\times3.125=0.625N$
Work done by frictional force= $F\times S=0.625\times100=62.5J$
