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如图所示，在倾角一定的固定斜面上有一竖直挡板，挡住一个重为G的光滑球，球对竖直挡板的作用力的大小也为G．若挡板改变方向变为垂直斜面挡住球，球对挡板的作用力又是多少？

答案

如图1所示，根据球的重力作用效果，是同时挤压斜面和挡板，故确定重力的两个分力方向分别垂直斜面和挡板．

G2=Gtgθ=G，则θ=45°

如图2所示，斜面与挡板所受的压力大小分别为：

N/1
=Gcos45°=
2
2
G，

N/2
=Gsin45°=
2
2
G．

答：球对档板的作用力为

2
2
G．

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