Labrador99
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Here's a place for anyone doing AH physics to discuss the course, ask questions you're stuck on, share advice for the assignment, and prepare for the final exam

How's everyone finding it so far?
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Hey234
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An object of mass 0.20 kg is connected by a string to an object of half its mass. The
smaller mass is rotating at a radius of 0.15 m on a table which has a frictionless surface.
The larger mass is suspended through a hole in the middle of the table.
Calculate the number of revolutions per minute the smaller mass must make so that the larger mass is stationary?

how to answer this question?
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Eimmanuel
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(Original post by Hey234)
An object of mass 0.20 kg is connected by a string to an object of half its mass. The
smaller mass is rotating at a radius of 0.15 m on a table which has a frictionless surface.
The larger mass is suspended through a hole in the middle of the table.
Calculate the number of revolutions per minute the smaller mass must make so that the larger mass is stationary?

how to answer this question?

Name:  circular_motion_01.JPG
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The above picture depicts what the problem is describing.
“An object of mass m2 = 0.20 kg is connected by a string to an object of half its mass. The smaller mass m1 is rotating at a radius of r = 0.15 m on a table which has a frictionless surface.”

The tension in the string is due to the weight of m2 and the centripetal force is provided by the tension to cause m1 to move in a circular motion of radius r. You should be able to write Newton’s 2nd law for m1 and solve for the angular velocity of m1 to find the number of revolutions per minute.
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Labrador99
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(Original post by Hey234)
An object of mass 0.20 kg is connected by a string to an object of half its mass. The
smaller mass is rotating at a radius of 0.15 m on a table which has a frictionless surface.
The larger mass is suspended through a hole in the middle of the table.
Calculate the number of revolutions per minute the smaller mass must make so that the larger mass is stationary?

how to answer this question?
:wavey: I've moved your question over into the new AH physics thread for this year
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Hey234
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(Original post by Labrador99)
:wavey: I've moved your question over into the new AH physics thread for this year
Thank you, i couldn't find the new thread for this year.
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Labrador99
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(Original post by Hey234)
Thank you, i couldn't find the new thread for this year.
No problem- I just created it
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Hey234
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During trial firing of Pioneer Moon rockets, one rocket reached an altitude of
125,000 km. Neglecting the effect of the Moon, estimate the velocity with which this
rocket struck the atmosphere of the Earth on its return. (Assume that the rocket’s path is
entirely radial and that the atmosphere extends to a height of 130 km above the Earth

Please don't answer this, I just need a direction of what theory should I think about here and how to approach this question, I think they are talking about impact velocity but that is not mentioned in the curriculum.
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Eimmanuel
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(Original post by Hey234)
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Please don't answer this, I just need a direction of what theory should I think about here and how to approach this question, I think they are talking about impact velocity but that is not mentioned in the curriculum.
I thought impact velocity or impact speed is typically found using conservation of energy or sometimes it also needs conservation of angular momentum. I would be very surprised conservation of energy is not covered in a typical A-level physics syllabus. However, not covering conservation of angular momentum is understandable.

As for this problem, you can solve it using conservation of energy. It is like throwing a ball upward and asking you what is the speed at certain height above the ground.
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tomctutor
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I'm still here tomctutor.
I think the above question is simply F= ma= mv^2/r etc, usual circular motion, where 'a' would be g= GM/r^2 but I might be wrong!
Last edited by tomctutor; 1 year ago
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rittyt
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Project Help:
I have three measurement uncertainties, two of them are insignificant... Do I still use the Squareroot uncertainty formula with that one uncertainty or do I just use that uncertainty as my main?
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Labrador99
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How's everyone feeling about the exam? Hope that the projects all got sent away without any issues
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tomctutor
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Has anyone got any concerns about this years AHPhysics exam?
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tomctutor
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(Original post by rittyt)
Project Help:
I have three measurement uncertainties, two of them are insignificant... Do I still use the Squareroot uncertainty formula with that one uncertainty or do I just use that uncertainty as my main?
No need to use \sqrt but should state why you are ignoring these quantities, less than 1/3rd ignore.
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Labrador99
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Good luck for the exam tomorrow!
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maxymoo
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Good luck everyone. Fc for a reasonable paper!
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Labrador99
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How did the exam go?
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maxymoo
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I think my ds thought ok- better than he thought it might, but has realised has made some silly mistakes so fc he has done ok.
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tomctutor
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(Original post by Labrador99)
How did the exam go?
Anyone got the paper scan or decent images then ill try look at it!
Last edited by tomctutor; 1 year ago
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Aj987654321
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Anyone got a copy of the paper
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