本题目来源于试卷: Space Time & Motion A.2 Forces & Momentum，类别为 IB物理学
[单选题]
A block of wood is placed on a roug q) ttb)- cifwwgdyu g88j1d)4 h inclined sur , uqus*d- g5esp( i2tfm lch36face. Which of the diagrams below corre li cgm5*h3pt sue s-f(qu,6d2ctly represents the forces acting on the block when it is at rest?
A.
B.
C.
D.
参考答案: A
本题详细解析:
Explanation:
Weight always acts vertically downwards. Normal reaction force is always normal (perpendicular) to the surface. In order to remain at rest, friction must act up the incline in order to keep the block from sliding down the incline under the action of the component of weight acting down the incline.
In diagram B, friction is acting down the incline. This will result in an acceleration down the incline.
In diagram C, the normal reaction is acting opposite to the weight whereas normal reaction must always be perpendicular to the contact surface.
In diagram D, weight is shown to act at an angle to the vertical, whereas weight always acts vertically downwards.
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