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Monday, October 20, 2014

1–48

1–48 Consider a 70-kg woman who has a total foot imprint
area of 400 cm2. She wishes to walk on the snow, but the
snow cannot withstand pressures greater than 0.5 kPa. Determine the minimum size of the snowshoes needed (imprint
area per shoe) to enable her to walk on the snow without
sinking.
ANS
1-48 The mass of a woman isgiven. The minimumimprintarea per shoe needed toenableher towalkon the snow withoutsinking istobe determined. Assumptions1 The weight of the person isdistributed uniformlyon the imprintarea of the shoes. 2 One footcarries the entire weightof a person during walking, and the shoe issized for walking conditions (rather than standing). 3 The weightofthe shoes is negligible. Analysis The mass of the woman isgiven tobe 70 kg. For a pressure of 0.5 kPa on the snow, the imprintarea of one shoe mustbe 2 m 1.37 =             ⋅ = = = 2 2 2 N/m 1000 kPa 1 m/s kg 1 N 1 kPa 0.5 ) m/s kg)(9.81 (70 P mg P W A Discussion Thisisa verylarge area for a shoe, and such shoes would be impracticaltouse. Therefore, somesinking of the snow should be allowed tohave shoes of reasonable size.

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