Physics

Problem

Two smooth reflecting boards are placed making an angle of

60^{\circ}

with each other. A narrow beam of sound strikes the first board with an angle of incidence of

20^{\circ}

and then gets reflected from the second board. What is the angle between the final beam and the original incident beam after the two reflections? a)

80^{\circ}

60^{\circ}

120^{\circ}

140^{\circ}