Hello graceyFirst, find the value of using the fact that when .

Then, writing the velocity as (where is the distance of the particle from O), solve the equation by integration, using your value of .

You know that when ; and you need the value of when .

For the last part, the acceleration is . So if you differentiate , you'll get a formula for in terms of . Use this to find when ; then plug this value of into your equation for to find the distance from O.

Can you complete it now?

Grandad