Question

A car misses a turn and sinks into a shallow lake to a depth of 8.9 m. If the area of the car door is 0.51 m2, what is the force exerted on the outside of the door by the water? Note: 1 atm = 101.325 kPa.

What is the force exerted on the inside of the door by the air, assuming the inside of the car is at atmospheric pressure? Think about what the occupant should do to get the door open.

Answer 1

p(h)=p0+D•g•h,
where D is the density of water.
p(8.9 )=101325+1000• (9.8) • (8.9)=188545 Pa
Force is pressure multiplied by area.
F(out)=p•A=188220 • (0.51)=96158 N
F(in)=p0•A=101325• (0.51)=51676 N
The door may be opened when p (in ) = p (out).
Wait the moment when the water gets into the car