A tornado passes in front of a building, causing the pressure to drop there by 25% in 1 second. Part A If a door on the side of the building is 8.1 feet tall and 3 feet wide, what is the net force on the closed door.

  F_net = 264, 26 pound

Explanation:

For this exercise we use Newton's second law

               F_net = F_int - F_outside

where the force can be found from the definition of pressure

              P = F / A

              F = P A

we substitute

               F_net = P_inside  A - P_outside A

               F_net = A (P_inside - P_outside)

indicate that the pressure on the outside is 25% less than the pressure on the inside

               P_outside = 0.25 P_inside

The area is

               A = L W

we substitute

              F_net = L W P_inside (1-0.25)

let's calculate

suppose the pressure inside is atmospheric pressure

              P_inside= P_atmospheric = 1,013 10⁵ Pa = 14.7 PSI

              F_net = 8.1 3 14.5 0.75

              F_net = 264, 26 pound

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