Tension and Centripetal Force in Circular Motion

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Lori

Homework Statement


Physics problem diagram: a ball of mass 3.0 kg hung by two wires from a horizontal arm on a vertical shaft, with labelled lengths 0.8 m, 1.0 m and 0.6 m, angle theta = tan^-1(0.6/0.8) = 36.9 degrees, and handwritten working T2 cos theta = mv^2/R giving T2 = 29 N; a free-body force diagram with T1, T2 and W is shown beside it.

Where does T2cos(theta) come from ? Isn't mv^2/R the centripetal force which is the tension of rope 2?

Homework Equations



Fc = mv^2/R

3. Solution

Wait! The horizontal component of the circle is the centripetal force? So that part is mv^2/R?

I got confused and thought the tension of rope 2 is actually the centripetal force. But if the x point of that tension is the centripetal force, i see how they got T2Cos

since cos(theta) = Xcomp/T2
i get cos(theta) = (mv^2/R)/T2

so that T2cos(theta)= (mv^2/R)[/B]
 
Attachments
  • Physics problem diagram: a ball of mass 3.0 kg hung by two wires from a horizontal arm on a vertical shaft, with labelled lengths 0.8 m, 1.0 m and 0.6 m, angle theta = tan^-1(0.6/0.8) = 36.9 degrees, and handwritten working T2 cos theta = mv^2/R giving T2 = 29 N; a free-body force diagram with T1, T2 and W is shown beside it.
    upload_2017-11-4_20-55-16.png
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  • Handwritten solution on a physics problem sheet: a ball of mass 3.0 kg on two wires from a horizontal arm on a rotating vertical shaft, with the force diagram, tan(theta) = 0.6/0.8 = 36.9 degrees, and T2 cos(theta) = mv^2/R giving T2 = 29 N.
    upload_2017-11-4_20-57-2.png
    37.6 KB · Views: 1,325
Last edited by a moderator:
Yes, the ball is moving in a horizontal circle as shown below. The centripetal force must point from the ball toward the center of the circle. You can see that the x-component of T2 is the only force acting on the ball in this direction. So, the centripetal force is T2cosθ.
Diagram of a conical pendulum: a ball on a string at 1.0 m length, at angle θ from a vertical rod, with a horizontal bar of 0.8 m and a 0.6 m segment, a red horizontal circular path, tension T2 along the string, and its horizontal component T2 cos θ pointing toward the axis.
 
Attachments
  • Diagram of a conical pendulum: a ball on a string at 1.0 m length, at angle θ from a vertical rod, with a horizontal bar of 0.8 m and a 0.6 m segment, a red horizontal circular path, tension T2 along the string, and its horizontal component T2 cos θ pointing toward the axis.
    upload_2017-11-4_20-43-59.png
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TSny said:
Yes, the ball is moving in a horizontal circle as shown below. The centripetal force must point from the ball toward the center of the circle. You can see that the x-component of T2 is the only force acting on the ball in this direction. So, the centripetal force is T2cosθ.
View attachment 214370
Thank you. Your drawing really made sense of this all!