有條物理既問題唔係好明( 求解釋) THANK?

A 45 kg block rests on an inclined plane of 30. The coefficient of static friction is 0.25 and the coefficient of kinetic friction is 0.2. Find the smallest value of P required :

to start the block up the plane;

ANS:

Resolve forces along the plane

P=F+Mgsin30<<點解係SIN 30 唔係COS 30??

N=Mgcos30<??

F=Us N

P=Mgsin30-Us(Mgcos30)<<?

P=45x9.81x(0.25xcos30+sin30) 點解係X cos30+sin30<? 唔係好明 有附圖

Resolve forces along the plane

Attachment image

3 個解答

評分
  • 5 年前
    最愛解答

    P係頂住"SIR" 落黎個力,

    咁地心吸力,Mg, 拆力咪有個"SIR"落去既力, 果個就sin30, 同p相反既,

    另一個力就係N, 係action and reaction個力, 咪cos30

  • 5 年前

    我想問係咪Mg 果到拆多2支力出黎

  • 5 年前

    a

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