Methods of momentum

In this case the angular momentum about G remains constant.

Illustrative examples

Example 1:

In turbine, a jet of water is made to impinge on the vanes of turbine and get deflected by a certain angle. During this process, a force is exerted by the jet on the vane and that causes rotation of the turbine. The force exerted by the jet on the vane can be determined by applying momentum equations. This is illustrated.