Liquid helium is stored at its boiling point temperature of 4.2K in a shperical container(r=0.30m).The container is a perfect blackbody radiator.The container is surrounede by a sherical shield whose temperature is 77k.A vacuum exists in the space between the container and the shield.The latent heat of vaporization for helium is 2.1X10000.What mass of liquid helium boils away thruogh a venting valve in one hour?
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