Please help in this problem.. Here's the problem:

A body rises vertically from earth according to the law S= 64t - 16t^2. In here, I need to show or prove that it has lost one-half its velocity in the first 48ft. Of rise.

Another thing.. can you please check if my answer in this problem is correct.. :)

A particle is moving along a horizontal line according to the formula S= 1/3 t^3 - 1/2 t^2 - 2t + 2 whose S feet is the distance of the particle from the origin at time t(secs).

a.) what is the instantaneous velocity of the particle at t=2?

my answer: v=0

b.) when is the particle is at rest? When v=0, t>2 and t>-1

c.) when is the particle moving to the right? When v>0.

Hope you can help me. Thanks a lot.