i think we ca not bend our arm if a light wooden plank is tied to our arm because it stops our arm and our muscle parts from being bending. it keeps our arm straight.
     i hope that my answer will help u...............................^_^
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we cannot bend our arm because there is not joint the light wooden plank here acts as the bone and it does not allow our arm to bend cause there is no joint in the wooden. so to bend our arms we need joints so it is not possible to bend our hand .

hope so my answer is useful.... ^_^ !!
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