Conservation of energy and centripital force

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Homework Help Overview

The problem involves a mass sliding inside a hoop and requires calculating the force exerted by the mass on the hoop at a specific angle, using principles of conservation of energy and centripetal force.

Discussion Character

  • Exploratory, Conceptual clarification, Problem interpretation, Assumption checking

Approaches and Questions Raised

  • Participants discuss the use of trigonometry to find the distance of the mass below the hoop and the application of conservation of energy to determine the speed at the given angle. Questions arise regarding the accuracy of the free body diagram and the components involved in the centripetal force equation.

Discussion Status

Some participants are seeking clarification on the setup of the problem and the correctness of the equations used. There is an ongoing exploration of the free body diagram and the forces acting on the mass, with no clear consensus yet on the next steps.

Contextual Notes

Participants are working within the constraints of a homework problem, which may limit the information available and the assumptions that can be made about the system.

Megz27
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The Question is:

A mass M of 5.00×10-1 kg slides inside a hoop of radius R=1.50 m with negligible friction. When M is at the top, it has a speed of 5.65 m/s. Calculate size of the force with which the M pushes on the hoop when M is at an angle of 27.0 degrees.

My workings thus far:

1st i know i have to use the radius and theta to get the distance of the mass below the hoop
then i have to use the speed at the top and the conservation of mechanical energy to get the speed of the mass at theta
then i make a fbd and get the normal force

so
using trig
1.5 cos 27= x
x= 1.3365m (distance under center of hoop)
distance from bottem then equals 0.1635 m as the hoop is 1.5 m in radius

so using conservation of energy i get
total energy top= total energy bottem
potentical energy top + kE top = pot Energy bottem + Ke bottem
mgh + 1/2 mv^2 = mgh+1/2mv^2 (all masses cancel out
(9.81)(3) +1/2(5.65)^2 = (9.81)(0.1635) + 1/2 v^2
solve for v = 5.88223 m/s

so the speed at theata is 5.88223 m/s, then using centripical force =mv^2/r we can get 23.067 N for the force.

Then we draw a free body diagram and we get that Fc=Fn (what were looking for)+ Fg
This is were i get stuck..
Help from here??
 
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Welcome to PF!

Megz27 said:
… when M is at an angle of 27.0 degrees

Then we draw a free body diagram and we get that Fc=Fn (what were looking for)+ Fg …

Hi Megz27! Welcome to PF! :smile:

i] 27.0 degrees from what? :confused:

ii] Fc = Fn + Fg is not correct.
 
27 degress from the bottem of the circle..

how would you approach the FC is that is not correct?
 
Megz27 said:
then i make a fbd and get the normal force

What does your fbd look like?

In which direction are you taking components?

What equation does it give you? :smile:
 

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