Which of these questions is a scientific question about skateboarding?
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a. how fast does a skateboard move at the bottom of a ramp?
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b. should skateboarding be allowed in shopping malls?
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c. what is the best trick to do while moving backward?
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d. which color of wheel looks best?

Arigid tank is divided into two equal parts by a partition. one part of the tank contains 3 kg of compressed liquid water at 400 kpa and 60°c while the other part is evacuated. the partition is now removed, and the water expands to fill the entire tank. determine the entropy change of water during this process, if the final pressure in the tank is 40 kpa. use steam tables.