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Ramp Problems

Hi, I have a ramp problem question that I don't think makes sense..
Question:
A 1kg block is placed on a ramp where the angle at which the slope is increased by 1 degree until it falls down the ramp. The block falls down the ramp when the angle is 25 degrees, find the a) force of gravity, b) normal force c) applied force, d) force of static friction and e) the coefficient of static friction... I know how to get the force of gravity, but none of the others... ????
 

HallsofIvy

Science Advisor
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The gravitational force is, of course, -mg.

The "normal force" is the force perpendicular to the surface. Set up a diagram with the gravitational force vector downward as the hypotenuse of a right triangle, one leg perpendicular to the surface and one leg parallel to it. You can show that the angle of that triangle at the surface is the same as the angle the surface makes with the horizontal: in this case 25 degrees: use that to show that the normal force is -mg cos(25). The force along the ramp is
-mg sin(25).

If the mass does not begin to move until the ramp is at a 25 degree angle, then the friction force at that angle must be exactly enough to offset the force along the ramp: the friction force is
mg sin(25).

The friction force is given by the "coefficient of friction" times the normal force. Since you know that the normal force is -mg cos(25) and the friction force is mg sin(25): the coefficient of friction must be -sin(25)/cos(25).

I don't see any "applied force" here.
 

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