一物體質量m在水平桌面上以一力F(與水平成30度之仰角)拉之

Horizontal pulling force = F.cos(30)

Let R be the normal reaction, then
R + F.sin(30) = mg where g is the acceleration due to gravity
hence, R = mg - F.sin(30)

Frictional force = (uk).R = (uk).[mg - F.sin(30)]
Net pulling force = F.cos(30) - (uk).[mg - F.sin(30)]
= F(cos(30) + (uk).sin(30)) - (uk).mg
Acceleration = net force/mass = F(cos(30) + (uk).sin(30))/m - (uk).g



2013-01-14 07:50:24 補充：
cos(30)= (1/2).square-root(3) and sin(30) = 1/2

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