First, you find the pressure experience by the car at that depth. This pressure is called the hydraulic pressure with the equation: P=density*gravity*depth. The density of water is 1000 kg/m^3; the acceleration due to gravity is 9.81 m/s^2. So, we need a value for the depth. Suppose, the car was underwater 6 m deep. Then the pressure would be:
Pressure = 1000 kg/m3*9.81 m/s^2*6m = 58,860 Pascals
Pressure, by definition, is the force over unit area. Since we know the are of the circular window, we can therefore determine the force exerted by the water to the car's window.
P =F/A
P=F/(π*(0.35/2)^2)
58,860 = F/0.0962
F = 5,663 Newtons
