Answer :
1. x = 2.3 cos(ωt + Ф)
2. v = -2.3ω sin(ωt + Ф)
for: t = 0 , x = 0 ⇒ v = 10
Ф = π/2
now solve second equation for ω
2. v = -2.3ω sin(ωt + Ф)
for: t = 0 , x = 0 ⇒ v = 10
Ф = π/2
now solve second equation for ω