The question is, "A particle of mass 10kg is at rest on a rough plane inclined at 30° to the horizontal. A horizontal force of magnitude 10N acts on the particle. a) Find the magnitude of the friction force on the particle."(adsbygoogle = window.adsbygoogle || []).push({});

URL TO IMAGE (I added the green to help you understand why I am confused): i209.photobucket.com/albums/bb180/newguyjb/forcesdiagram.jpg

The book provides the answer with the working, which is:

F+10cos30°=98sin30°

F=98sin30°-10cos30°

=40.3N

However, I don't understand how they have decided that it is 10cos30°. On the diagram I provided (which is the link) in green the area which is not in the diagram in the book, but which relates to why I am confused as to why it is 10cos30°. Could someone explain why it is 10cos30°.

Thanks for any help.

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# Homework Help: Particle force question

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