While deriving an expression for loss of head due to a sudden expansion in a pipe, in addition to the continuity and impulse-momentum equations, one of the following assumptions is made :

• Head loss due to friction is equal to the head loss in eddying motion
• The mean pressure in eddying fluid is equal to the downstream pressure
• The mean pressure in eddying fluid is equal to the upstream pressure
• Head lost in eddies is neglected