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**The question goes as follows..:**

A car driver has an accident and drives into a lake. The car sinks to the bottom. The distance from the car door to the water surface is 10m. The car door is 0.9m wide and 1.3m tall. Assume that the car door can be approximated as a vertical rectangular plate and that the car is filled with air.

A) Calculate the pressure force acting on the door

A car driver has an accident and drives into a lake. The car sinks to the bottom. The distance from the car door to the water surface is 10m. The car door is 0.9m wide and 1.3m tall. Assume that the car door can be approximated as a vertical rectangular plate and that the car is filled with air.

A) Calculate the pressure force acting on the door

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**The solution manual solves the problem by calculating the hydrostatic force halfway down the car door,**

i.e. F = rho*g*(10+0.5*1.3) / 1.3*0.9

Isn't this wrong? My idea was to calculate the force by using the "prism" method, described here: https://en.wikipedia.org/wiki/Pressure_prism

i.e. F = rho*g*(10+0.5*1.3) / 1.3*0.9

Isn't this wrong? My idea was to calculate the force by using the "prism" method, described here: https://en.wikipedia.org/wiki/Pressure_prism