Tension and Newton's second law

AI Thread Summary
The discussion focuses on a physics problem involving a 7kg mass suspended from a string at an angle of 18 degrees. Participants analyze the forces acting on the mass immediately after it is released, emphasizing the role of tension and gravitational force. The equation Tcos18 - 68.6 = ma is derived to find the tension in the string, while questions arise regarding the acceleration of the mass and the direction of tension. Clarifications are sought on whether the acceleration is zero at the moment of release and the function of tension in the system. The thread highlights the complexity of free body diagrams and the interaction of forces in this scenario.
Touran Khan
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Homework Statement


A 7kg mass is hung from a 1.5 m long massless string. It is released from rest with the string displaced by
an angle of 18 degrees from vertical.
a) Make a free body diagram of the forces on the mass just after it is released.
b) Find the tension in the string.
c) Find the initial acceleration of the mass.

Homework Equations


F = ma

The Attempt at a Solution



b) Fy: Tcos18 - 68.6 = ma

Does ay = 0? And if it does then why exactly? Is it just cause they want the tension at that point so the object is not assumed to be moving?

However there will be an ax value right?

Thanks.
 
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In which direction does the tension act just after the mass is released? (What is the string actually accomplishing in this system?)
 
olivermsun said:
In which direction does the tension act just after the mass is released? (What is the string actually accomplishing in this system?)
 

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That is the diagram I made. Tension and Fg are in opposite directions which is how I got Tcos18 - 68.6 = ma
 
According to your diagram, Tension and Fg are not exactly in opposite directions. Just kind of.
 

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