A drinking straw 20 cm long and 3.0 mm in diameter stands vertically in a cup of juice 8.0 cm in diameter. A section of straw 7.0 cm long extends above the juice. A child sucks on the straw, and the level of juice in the glass begins dropping at 0.23 cm/s.
a) By how much does the pressure in the child's mouth differ from atmospheric pressure?
b) What is the greatest height from which the child could drink, assuming this same mouth pressure?