## Example: Water Jet Striking a Stationary Plate

**A stationary plate** (e.g.,, blade of a watermill) deflects water flow at a velocity of **1 m/s** and an angle of **90°**. It occurs at atmospheric pressure, and the mass flow rate is equal to **Q =1 m ^{3}/s**.

**Calculate the pressure force.****Calculate the body force.****Calculate the total force.****Calculate the resultant force.**

**Solution**

- The
**pressure force**is zero as the pressure at the inlet, and the outlets to the control volume are atmospheric. - As the control volume is small, we can ignore the
**body force**due to the weight of gravity. **F**= ρ.Q.(w_{x}_{1x}– w_{2x}) = 1000 . 1 . (1 – 0) =**1000 N**

**F**=_{y}**0**

**F**=**(1000, 0)**- The
**resultant force**on the plane is the same magnitude but in the opposite direction as the total force**F**(friction and weight are neglected).

The water jet exerts on the plate the force of 1000 N in the x-direction.