v=μ0 sin ωt (suppose t1 is the time of collision) 2μ0=μ0cosωt1⇒t1=3ωπNow the particle returns to equilibrium position at time t2=2t1 i.e 3ω2π with the same mechanical energyi.e. its speed will μ0 .Let t3 is the time at which the particle passes through the equilibrium position for the second time.∴ t3=2T+2t1=ωπ+3ω2π=3ω5π=35πkmEnergy of particle and spring remains conserved.