A point mass is subjected to two simultaneous sinusoidal displacements in x-direction x1(t)=A sin ωt and x2(t)=Asin (ωt+2π3). Adding a third sinusoidal displacement x3(t)=B sin(ωt+ϕ) brings the mass to a complete rest. The values of B and ϕ are
A, 4π3
As per the question, A sin ωt+A sin (ωt+2π3)+B sin (ωt+ϕ)=0⇒B sin (ωt+ϕ)=−[A sin ωt+A sin (ωt+2π3)]=−A[2sin (ωt+π3)cos π3]⇒B sin (ωt+ϕ)=−Asin (ωt+π3)=Asin (ωt+4π3)
Hence, B=A and ϕ=4π3