Discussion in 'Pre-Medical - MD' started by NubianPrincess, Jun 16, 2002.

1. ### NubianPrincess Perpetually Bored 7+ Year Member

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This is the question:
A box slides down a 30 degree ramp with an acceleration of 1.20m/s^2. Determine the co-efficient of kinetic friction between the box and the ramp.
The solution to this problem is <a href="http://physics.baruch.cuny.edu/summer2k2/sol0403.gif" target="_blank">here</a>.
I understand the theories involved, but my problem is I am unclear how to determine the components of the forces when the object is on an incline. I dont understand how to know that the component in the x direction is = Fg*sin30.
Please help me if you can, please? I understand where im getting stuck - the method seems to be to break the force of gravity down into x and y components, but I thought that the x componet would involve cos, not sin?????

2. ### Legend Super Senior Member 10+ Year Member

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Look at the 'triangle' in the diagram.

The component parallel to the inclined plane is the force you need to calculate friction coefficient.

3. ### moo 1K Member 10+ Year Member

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You can reason this out from simple geometry (similar triangles).

Sorry I can't be of more help but it's really hard to teach someone this stuff w/o drawing the diagrams.

4. ### Legend Super Senior Member 10+ Year Member

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</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by NubianPrincess:
but I thought that the x componet would involve cos, not sin?????[/QB]</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">If you rotate 'x-component' about 90 degrees, it becomes 'y-component'.

Look at the triangle carefully. That triangle seems somewhat inverted, right?

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