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A student of mass 50 kg is standing on both feet. Estimate the pressure exerted by the student on the Earth. Assume reasonable value to any quantity you need; justify your assumption. You may use g = 10 m/s2 , By what factor will it change if the student lies on back ? |
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Answer» Assume area of each foot = area of a 6 cm × 25 cm rectangle. ∴ Area of both feet = 0.03 m2 ∴ The pressure due to the student’s weight = \(\cfrac{mg}{A}\) = \(\cfrac{50\times10}{0.03} = 16.7\) kpa According to the most widely used Du Bois formula for body surface area (BSA), the student’s BSA = 1.5 m2 , so that the area of his back is less than half his BSA, i.e., < 0.75 m2 . When the student lies on his back, his area of contact is much smaller than this. So, estimating the area of contact to be 0.3 m2 , i.e., 10 times more than the area of his feet, the pressure will be less by a factor of 10 or more, [Du Bois formula : BSA = 0.2025 × W0.425 × H0.725 , where W is weight in kilogram and H is height in metre.] |
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