Q.Describe the state of oscillation if the phase angle is 1110°.

The phase (or phase angle) of an S.H.M. is the quantity (omega t + phi) -- the same reference angle used in the U.C.M.-projection picture. It is needed because neither displacement alone nor velocity alone fully specifies the "state" of an oscillation: at a given displacement (other than the extremes) there are two possible directions of velocity, and at a given speed (other than at the mean position) there are two possible positions, and both x and v repeat identically every cycle regardless. Phase, by contrast, increases continuously and without limit as time passes, so it uniquely pins down position, direction of motion, AND which oscillation (cycle number) the particle is currently in.

Four special phase values recur constantly: phase = 0 (or any multiple of 2pi) means the particle is at the mean position moving towards positive; phase = pi (or that plus a multiple of 2pi) means mean position moving towards negative; phase = pi/2 (plus a multiple of 2pi) means the positive extreme position; phase = 3pi/2 (plus a multiple of 2pi) means the negative extreme position. Interpreting a phase angle problem generally involves two steps: first strip off complete multiples of 2pi (or 360 degrees) to find both the "base" angle within one cycle and which oscillation number that represents, then use the sign/direction information given to resolve any remaining ambiguity (since sin^-1 and cos^-1 each have two solutions per cycle).