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HOMEWORK 20.B - SP 24
16 thoughts on “HOMEWORK 20.B - SP 24”
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This might be a dumb question, but I guess we're supposed to just assume W is the weight of the quarter-circle block? Since it doesn't say what W is anywhere in the problem and the wedge is typically assumed to massless?
That's what I would go with. I was just wondering about that, but I believe they imply that the block must have a mass because otherwise it won't apply a weight to the wedge, so there wouldn't be much of a problem to solve.
Also, this is kind of a spoiler for the problem, but what is the actual reason that forces alone can't just be used here? It just seems pointless to do a moment since I don't see why you couldn't just assume W is only acting down on the block.
Never mind just figured it out - it's due to the unknown reaction force at Ay making it impossible to solve for the final value.
So since it is stated that the surface between the wedge and the ground is smooth, does that mean that there will be no friction force at that surface?
Yes, no friction at that surface.
Would the reaction at the point of contact between the two objects only be perpendicular the surfaces, or would it have a parallel component as well?
I believe it's only perpendicular, because the normal force acts perpendicular to the surface (and since the force on the quarter-circle is equal and opposite that on the wedge, the force of the wedge on the quarter-circle would be perpendicular the surface of the wedge).
David Fall, the normal force would just be perpendicular yeah. Its like how if there was a bear eating apples on a ramp, the normal force would just be going perpendicular to the ramp.
I'm not sure we need to use a moment to calculate P, as the force equations for our wedge should give us an answer, along with factoring in W through the quarter circle equations. Thoughts?
I do think you need the moment equation when calculating it. I think you’ll have to many unknown variables if you don’t use the moment equation
I agree that you need to use a moment equation because you don't know the reactions at the pin on the quarter-circle.
What are the quarter-circle equations? Are those the equations for finding the centroid?
For finding the centroid of the quarter-circle, can we use the location given before in class, or do we have to show how this centroid is derived?
I didn't show how it is derived because it is a common centroid and they have already given it to us in class.
It's usually best to show all steps in preparation for exams, as partial credit is crucial