2
67kviews
Problems related to force exerted by Jet
5
3.3kviews

Q1) Find the force exerted by a jet of water of diameter 75 mm on a stationary flat plate, when the jet strikes the plate normally with a velocity of 20 m/s.

Solution: Given:

i) Diameter of jet, d = 75mm = 0.075mm

ii) Area, $a = \dfrac\pi4d^2 = \dfrac\pi4(0.075)^2 = 0.004417m^2$

iiii) Velocity of jet, v = 20m/s

The force exerted by the jet of water on a stationary plate is given by,

$F = \rho av^2$

$F = 1000\times 0.004417\times20^2 = 1766.8N$

Q2) A jet of water of diameter 50 mm strikes a fixed blade in such a way that the angle between the plate and the jet is $30^\circ$. The force exerted in the direction of jet is 1471.5N. Determine the rate of flow of water.

Solution:

Given:

i) Diameter of jet, d = 50mm = 0.05m

ii) Area, $a = \dfrac\pi4\times(0.05)^2 = 0.00163m^2$

iii) Angle,$\theta = 30^\circ$

iv) Force in the direction of jet,

$F_x = 1471.5N$

As force is given in (N), $\rho$ should be taken equal 1000 kg/m$^3$

$\therefore 1471.5 = 1000\times0.001963\times v^2\times \sin^230$

$\therefore v^2 = \dfrac {150}{0.05} = 3000$

$v = \sqrt{3000} = 54.77m/s$

Discharge, Q = Area $\times$ velocity

$Q=0.001963\times 54.77=0.1075m^3/s$

Q3) A jet of water of diameter 50 mm moving with a velocity of 40 m/s, strikes a curved fixed symmetrical plate at the centre. Find the force exerted by the jet of water in the direction of the jet, if the jet is deflected through an angle of 120$^\circ$ at the outlet of the curved plate.

Solution:

Given:

i) Diameter of jet, d = 50mm = 0.05m

ii) Area, $a = \dfrac \pi4(0.05)^2 = 0.001963m^2$

iii) Velocity, v = 40m/s

$\therefore$ To find $\theta$, use equation

$180-\theta$ = given angle

$180-\theta = 120$

$\therefore, \theta = 180-120 = 60^\circ$

$\therefore F_x = \rho av^2[1+\cos\theta]$

$F_x = 1000\times 0.001963\times40^2\times[1+\cos 60^\circ]$

$F_x = 4711.5N$

Q4) A jet of water of diameter 75 mm moving with a velocity of 30 m/s, strikes a curved fixed plate tangentially at one end at an angle of 30$^\circ$ to the horizontal, the jet leaves the plate at an angle of 20$^\circ$ to the horizontal, find the force exerted by a jet on the plate in the horizontal and vertical direction.

Solution:Given:

i) Diameter of jet, d = 75mm = 0.075m

ii) Area, $a = \dfrac\pi4\times(d^2)$

$a = \dfrac\pi4\times(0.075)^2 = 0.004417m^2$

iii) Velocity, v = 30m/s

iv) Angle made by the jet at inlet tip with horizontal, $\theta = 30^\circ$

v) Angle made by the jet at outlet tip with horizontal, $\phi = 20^\circ$

$\therefore F_x = \rho av^2[\cos\theta+\cos\phi]$

$F_x = 1000\times0.004417\times30^2\times[\cos30^\circ+\cos20^\circ]$

$F_x = 7178.2N$

$F_y = \rho av^2[\sin\theta-\sin\phi]$

$F_y = 1000\times0.004417[\sin30-\sin20]\times30^2$

$F_y = 628.13N$