A particle executing S.H.M. of amplitude 4 cm and T = 4 sec. The time taken by it to move from positive extreme position to half the amplitude is
1 sec
13sec
23sec
32 sec
Equation of motion y = a cos ωt
⇒ a2 = a cos ωt ⇒cos ωt = 12 ⇒ωt =π3
⇒ 2πtT = π3 ⇒ t = π3×T2π = 43×2 = 23sec