Question

A tornado rips *** a 100 m2 roof with a mass of 1000 kg. What is the minimum vacuum pressure needed to do that if we neglect the anchoring forces ?

Answer 1

The net force on the roof is the difference between the forces on the two sides as the pressure times the area

F = Pinside A – PoutsideA = ∆P A

That force must overcome the gravitation mg, so the balance is

∆P A = mg

∆P = mg/A = (1000 kg × 9.807 m/s2 )/100 m2

= 98 Pa = 0.098

Remember that kPa is kN/m2.