Position linked to Angle Control

With this expression, you can animate an object along only one axis, using a Slider, and then change the direction of motion using Angle Control. Applies to the layer’s Position parameter.

p = effect("Slider Control")("Slider"); 
a = effect("Angle Control")("Angle"); 
r = degreesToRadians(a-90);
x = p*Math.cos(r);
y = p*Math.sin(r);
value + [x,y]

After Effects, Expression