[amherst]

A 1lb bird sits on a telephone wire 50 ft from each end. If the wire sags by 2 inch find the tension in the wire assume the wire is weightless. :)

[ebaines]

Draw a free-body diagram of the system - the wire, bird, and end supports, including the components of force. See attached. From symmetry you can determine the upward component of force at the end supports, F_y. Next determine the horizontal force at the end support F_x based on the geometry of similar triangles (the horizontal and vertical components of the wire sag form a triangle that is similar to the horizontal and vertical components of the force at the end support). So now you have F_y and F_x, and can determine the total force F at the end support. This is the tension in the wire.