A uniform capillary tube, colsed at one end, contained air which is trapped by a thread of mercury 85mm long. When the tube was held horizontally, the length of the air column was 50mm. When it was held vertically with the closed end downwards, the length was 45mm. Find the atmospheric pressure in Nm-2 .
(Take g= 10ms-2).
I know P1V1=P2V2 but I am not sure which is which and how to solve it mathematically with so many different units of measurement. I am confused. Please enlighten me what are the steps in resolving this.

Thanks.

Assess the risks arising from actual or poetntial exposure to noise and vibration

A real life situation which is related to heat is needed to conduct an experiment. What I choose is about a clothe to dry ( evaporate ). I've recently conducted an experiment about the rate of evaporation of water by placing a beaker containing water under a fan of different speeds. Can this relate to the convection? Convection of air?