Tension and Newton's second law

[Touran Khan]

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 a_y = 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 a_x value right?

Thanks.

 

[olivermsun]

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

 

[Touran Khan]

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

 

[Touran Khan]

That is the diagram I made. Tension and Fg are in opposite directions which is how I got Tcos18 - 68.6 = ma

 

[olivermsun]

According to your diagram, Tension and Fg are not exactly in opposite directions. Just kind of.