**Finding the Total Pressure on a Rectangular Plate Immersed in Water**

To find the total pressure on a rectangular plate immersed in water, we can use the concept of hydrostatic pressure. Hydrostatic pressure is the pressure exerted by a fluid at rest due to the weight of the fluid above it.

**Given Data:**
- Dimensions of the rectangular plate: 2m x 4m
- Two sides of the plate are parallel to the water surface
- The plate is 2.5m below the water surface
- Specific weight of water: 9.8 kN/m³

**Calculating the Total Pressure:**

To calculate the total pressure on the rectangular plate, we need to consider the pressure exerted by the water column above it.

1. Calculate the depth of the plate below the water surface:
- The plate is 2.5m below the water surface.

2. Calculate the pressure at the depth of the plate:
- The pressure at any depth in a fluid is given by the formula: P = ρgh
- P: Pressure
- ρ: Density of the fluid
- g: Acceleration due to gravity
- h: Depth below the surface
- In this case, the fluid is water and its specific weight is given as 9.8 kN/m³.
- Therefore, the pressure at the depth of the plate is: P = (9.8 kN/m³) * (2.5m) = 24.5 kN/m².

3. Calculate the total area of the plate:
- The rectangular plate has dimensions 2m x 4m.
- Therefore, the total area of the plate is: A = (2m) * (4m) = 8m².

4. Calculate the total pressure on the plate:
- The total pressure on the plate is the product of the pressure at the depth and the total area of the plate.
- Therefore, the total pressure on the plate is: P_total = (24.5 kN/m²) * (8m²) = 196 kN.

**Conclusion:**

The total pressure on the rectangular plate, which is vertically immersed in water with two sides parallel to the water surface and 2.5m below it, is 196 kN. This calculation is based on the hydrostatic pressure concept, considering the specific weight of water as 9.8 kN/m³.

A rectangular plate 2m×4m is vertically immersed in water is such a way that the 2 metres side is parallel to the water surface and 2.5 metres below it. Determine: i) The total pressure on the rectangular plate. ii) Centre of pressure of the rectangular plate.