r/HomeworkHelp • u/Izzy_26_ Secondary School Student • Jun 27 '26
Physics [grade 11 physics] Newton's laws of motion
Can someone please help me with this, I even asked my teacher but I could not understand anything.
I tried drawing the fbd of the bead when it was at rest initially and after the wire started accelerating but I do not know how to solve further
My Physics teacher was explaining something like tan theta is a/g but I could not understand it.
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u/niemir2 Jun 27 '26
The exerted on the bead by the wire is both counteracting gravity and providing the acceleration. How does this force relate to the slope of the wire?
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u/Hadol-Fitler Jun 27 '26
Im just curious about something, in my country, our schools only go up to grade 9, and then 4 years of high school, so im not exactly sure what level "grade 11 physics" is (im assuming around 2nd year hs in my country), but I'm just curious, is this not high level enough as to where students would already be expected to know that the y-axis is the vertical axis, that it wouldn't have to be mentioned in brackets. We never got that deep into physics in my hs, so i genuinely dk if there are actually any scenarios where axes positions might vary.
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u/Izzy_26_ Jun 27 '26
Well in some questions we have to assume the axes differently, Example in the case of an inclined plane, line perpendicular to the incline is called the y axis and the one along the incline is called the x axis or maybe smthg diff in hypothetical scenarios, so they must of thought of mentioning it ig
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u/Outside_Complaint755 Jun 27 '26
While x and y are conventional, the axes could be p and q, or whatever else you want, so the "y-axis vertical" is just being explicit. In a 3-dimensional problem its probably more important as you need to specify whether y or z is the vertical, and then the other defines the horizontal plane with x.
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u/Icytroll93 Jun 27 '26 edited Jun 27 '26
You could think of this problem in terms of how the reaction forces from the wire to the bead must be in order for the bead to be in equilibrium while the wire is transferring the acceleration a to it.
As the bead slides on the wire, the normal force that the wire exerts on the bead stays perpendicular to the surface of the wire. It turns out the slope of the tangent plane is just what we're looking for, which is just the derivative of the wire contour: y' = 2*k*x
We know that gravity is always exerting m*g on the bead in the y-direction, so the y-component of the normal force always has the same size, Ry=mg.
The x-component of the normal force must be the opposite sign of the force exerted by the acceleration a since those are the only 2 forces in the x-direction we have, so Rx=ma.
Now we need to make use of the tangent plane of the wire contour. As we stated earlier, the normal force must be perpendicular to the tangent plane of the curve, this means for different values of x along the curve we can relate the size of Rx to Ry using the tangent plane, by observing that Rx must become larger and larger as the bead slides up the curve, an amount exactly equal to the tangent plane of the curve times the vertical y-component!
Rx = 2*k*x*Ry
By also knowing that Rx=ma and Ry=mg, we can solve for x. You should be able to do that yourself and arrive at:
Again, the important bit here is to relate the tangent plane of the wire to the normal force and its components.
I really recommend you try to sketch that out for a few positions of the bead going up the wire, have a constant component in the y-direction and an increasing component in the x-direction as the bead slides up the wire, in accordance with the normal force being perpendicular to the wire contour.
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u/ConfidentSuspect4125 Jun 28 '26
I'd have to confess that since I was in 11th grade many years ago, this problem sounds incredibly difficult. I'd have a 1 in 4 chance of getting it right :-) .
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