The circular clapper on the air side of a dry pipe sprinkler valve has a diameter of 10 in (25cm). what force will be acting on this clapper due to an air pressure of 40psi(3bar)?
correct answer from back of book is: 3141.6lbs
how do i get this answer? show me all the formulas and steps you took to get this answer,

Asmall electric heater, immersed in 80g of water in a calorimeter of 40j/k raises the temperature from 10.5 degree celsius to 25 degree celsius in 12 minutes. using the same apparatus with 50g of oil instead of water, it is found that the temperature of oil rises from 7 degree celsius to 27 degree celsius in 10 minutes. find specific heat capacity of the oil.