質量m的物體 - Ans.fyi 參考答案

質量m的物體

2013-01-06 7:13 am

質量m的物體靠於鉛直牆上與牆間之靜摩擦係數為us 今施ㄧ水平力F於物體使物體不滑下下列何者正確

1.F=mg

2.mg=usF

3.牆與物體間之磨擦力為mg

4.牆施於物體之淨力(合力)為F*根號1+us平方

5.若物體與牆無磨擦則F無論多大均不能平衡

錯誤的地方如何修正

更新1:

答案是3.5

回答 (1)

天同

2013-01-06 8:42 am

✔ 最佳答案

Statement 2 is correct.
Friction Ff = mg
but Ff = (us)R = (us)F
where R is the normal reaction, which acts horizontally opposite to direction of F

Statement 3 is correct.
The frictional force is acting upward, which balances the downward weight mg

Statement 4 is correct
Net force = square-root[R^2 + Ff^2] = square-root[R^2 + (us,R)^2]
= R.square-root(1+us^2) = F.square-root(1+us^2)

Statement 5 is correct.
Fis horizontally acting, it cannot balance the vertically acting weight mg

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