Circular Motion: Calculate Velocity & Period

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Homework Help Overview

The problem involves a mass being twirled in a horizontal circle, with specific parameters including the mass, string length, and angle of the string. Participants are tasked with calculating the velocity and period of the mass's motion.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the calculation of the radius based on the angle and string length, the role of tension in the string, and the components of forces acting on the mass. There are questions about the interpretation of the angle's reference point and the correctness of the initial calculations.

Discussion Status

Some participants affirm the correctness of the original poster's method, while others seek clarification on the angle's reference. There is an ongoing exploration of the implications of the tension and its components in the context of circular motion.

Contextual Notes

Participants note the importance of understanding the angle's reference point and the balance of forces involved in the motion, which may affect the calculations. There is also mention of the mass's cancellation in the equations, suggesting a potential simplification in the problem-solving approach.

runningirl
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Homework Statement



A person is twirling a .7 kg mass over their head. The mass is attached to a string that is 1.5 m long. The mass spins in a HORIZONTAL circle. The string makes a 60 degree angle. Calculate the velocity of the mass, and then the period, that is necessary in order to make this work.

Homework Equations





The Attempt at a Solution



1.5*((sqrt3)/2) = 1.3 m=r
9.8(.7) sqrt3=11.88
F=mv^2/r
11.88=.7(v^2)/1.3
v=4.697 m/s

T=2*pi*r/V
=2*pi*1.3/4.697
=1.738 s?

i don't know if my method is correct.
 
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runningirl said:

The Attempt at a Solution



1.5*((sqrt3)/2) = 1.3 m=r

This part is correct.

There is a tension acting in the string. The vertical component of the tension is balancing out the weight of the mass while the horizontal component is providing the centripetal force. You need to get the value of this tension (which is easily done from the vertical component part)
 
Your method looks correct. What problem do you have?
 
runningirl said:
The mass spins in a HORIZONTAL circle. The string makes a 60 degree angle.


A 60 degree angle to relative to what? The person spinning the mass or to the horizontal circle.

If your angle is 60 degrees relative to the person, then your answer is correct.

You might notice that the mass is going to cancel out and you could do this problem using just the acceleration, but, other than that, your approach is correct.
 
it makes a degree relative to the person spinning.

thanks!
 

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