http://twu.tennis-warehouse.com/learning_center/hockeyphysics.php

It's All About Balance  

​A player produces a large force on the stick which therefore rotates at a certain angular velocity depending on the force around a fixed axis.  The result of this is the propulsion of the puck in a forward direction.  

The motion of the stick can be reduced to the following equation where T is torque, and I0 is the moment of inertia.
​​τ = FR - k(y - x)L = I0(dω/dt) = (I0/L)(du/dt)

​Final speed of the puck is dependent on the speed of the player and the time of contact with the puck.  In the event that the player is traveling 3 m/s at the time of content, 3 m/s will simply be added to the final speed of the puck. 

There is also a slight curvature in the blade of a player's stick as well.  This also provides an additional source of elastic energy when a shot is taken.