How Can You Calculate Plane Acceleration with a Watch on a String?

[engineer2010]

Another Problem

A watch is tied to a string on an airplane. As the airplane takes off the string makes an angle of 25* to the vertical. The acceleration takes about 18s. What is the acceleration of the plane.

I drew a free body diagram, but I am confused as to how I would solve this without knowing the mass of the watch or the tension of the string.

 

[Doc Al]

Just call the tension T and the mass m and solve for the acceleration.