The formula to calculate the velocity of the particle at the mean position is given by
V=Aω...(1)
From equation (1), it follows that
10=4×ω⇒ω=25rads−1
The formula to calculate the velocity of the particle at any instantaneous position x can be expressed as
v=ωA2−x2...(2)
From equation (2), it follows that
5=2542−x2⇒x2=16−4=12⇒x=12cm
Hence, α=12.