# Physics

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Continuously running exhaust hoods in a university chemistry building keep the inside air pressure slightly lower than outside. A student notices that a 175 N force is necessary to start opening a 1.2 m by 2.3 m door. The door is hinged on one of its 2.3 m vertical sides, and the handle is mounted on the other side. What is the pressure difference between inside and outside? Give in pascals and as a fraction of atmospheric pressure. Hint: Think about torque.

• Physics -

The torque about the hinge due to the applied force on the handle equals the reverse torque due to the pressure difference. The pressure acts as if applied at the centroid of the rectangular door.

175*1.2 = (deltaP)*1.2*2.3*0.6

deltaP = 126 N/m^2 (Pascals)

Divide that by atmospheric pressure, in Pa, for the answer to the last part.

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