Why Is My Approach to Solving Physics Homework Incorrect?

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AI Thread Summary
The discussion centers on a physics homework problem involving the dynamics of a mass on a string. The initial approach incorrectly assumes that the tension in the string equals the weight of the mass. Participants suggest that the correct method involves applying Newton's second law separately to both vertical and horizontal forces. This approach will clarify the relationships between the forces and lead to the correct solution. Properly analyzing the forces is essential for solving the problem accurately.
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Homework Statement


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Homework Equations


5d423445741ddd2681bf2639f9b0bd89.png



The Attempt at a Solution



The way I understood is it is by taking ma and setting it equal to mv^2/r and solving for v. With this I got answer choice number 9, sqrt(glsinTHETA). But it's wrong. Can anyone direct me in the right direction to solving this deceptively easy problem? Thanks in advance.
 
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Garen said:

Homework Statement


2qbgkr5.png



Homework Equations


5d423445741ddd2681bf2639f9b0bd89.png



The Attempt at a Solution



The way I understood is it is by taking ma and setting it equal to mv^2/r and solving for v. With this I got answer choice number 9, sqrt(glsinTHETA). But it's wrong. Can anyone direct me in the right direction to solving this deceptively easy problem? Thanks in advance.
You're on the right lines. However, you incorrectly assume that the tension in the string is mg.
 
Hootenanny said:
You're on the right lines. However, you incorrectly assume that the tension in the string is mg.

So you're saying that I set mv^2/r equal g/cosTHETA ?
 
Garen said:
So you're saying that I set mv^2/r equal g/cosTHETA ?
No. Start by writing down two equations: one for the requirement of the sum of the forces in the vertical plane, and one for the sum of the forces in the horizontal plane. In otherwords, apply Newton's second law seperately to the vertical and radial planes.
 

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