Dynamics
Application of the Momentum Equation
6.1
The figure below shows a smooth curved vane attached to a rigid
foundation. The jet of water, rectangular in section, 75mm wide and 25mm
thick, strike the vane with a velocity of 25m/s. Calculate the vertical
and horizontal components of the force exerted on the vane and indicate in
which direction these components act.
[Horizontal 233.4 N acting from right to left. Vertical 1324.6 N acting
downwards]
6.2
A 600mm diameter pipeline carries water under a head of 30m with a
velocity of 3m/s. This water main is fitted with a horizontal bend which
turns the axis of the pipeline through 75 (i.e. the internal angle at the
bend is 105). Calculate the resultant force on the bend and its angle to
the horizontal.
[104.044 kN, 52 29']
6.3
A horizontal jet of water 2103 mm2 cross-section and
flowing at a velocity of 15 m/s hits a flat plate at 60 to the axis (of
the jet) and to the horizontal. The jet is such that there is no side
spread. If the plate is stationary, calculate a) the force exerted on the
plate in the direction of the jet and b) the ratio between the quantity of
fluid that is deflected upwards and that downwards. (Assume that there is
no friction and therefore no shear force.)
[338N, 3:1]
6.4
A 75mm diameter jet of water having a velocity of 25m/s strikes a flat
plate, the normal of which is inclined at 30 to the jet. Find the force
normal to the surface of the plate.
[2.39kN]
6.5
The outlet pipe from a pump is a bend of 45 rising in the vertical plane
(i.e. and internal angle of 135). The bend is 150mm diameter at its inlet
and 300mm diameter at its outlet. The pipe axis at the inlet is horizontal
and at the outlet it is 1m higher. By neglecting friction, calculate the
force and its direction if the inlet pressure is 100kN/m2 and
the flow of water through the pipe is 0.3m3/s. The volume of
the pipe is 0.075m3.
[13.94kN at 67 40' to the horizontal]
6.6
The force exerted by a 25mm diameter jet against a flat plate normal to
the axis of the jet is 650N. What is the flow in m3/s?
[0.018 m3/s]
6.7
A curved plate deflects a 75mm diameter jet through an angle of 45. For a
velocity in the jet of 40m/s to the right, compute the components of the
force developed against the curved plate. (Assume no friction).
[Rx=2070N, Ry=5000N down]
6.8
A 45 reducing bend, 0.6m diameter upstream, 0.3m diameter downstream, has
water flowing through it at the rate of 0.45m3/s under a
pressure of 1.45 bar. Neglecting any loss is head for friction, calculate
the force exerted by the water on the bend, and its direction of
application.
[R=34400N to the right and down, q = 14]
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