Mechanics Question - Please help!?

A body is falling through a liquid, and the distance fallen is modelled by the formula s=48t-t^3 until it comes to rest, where 's' centimetres is the distance fallen and 't' seconds is the time. Find a) the velocity when t = 1 b) the initial velocity c) the acceleration when t = 1 d) the time... show more A body is falling through a liquid, and the distance fallen is modelled by the formula s=48t-t^3 until it comes to rest, where 's' centimetres is the distance fallen and 't' seconds is the time. Find
a) the velocity when t = 1
b) the initial velocity
c) the acceleration when t = 1
d) the time when the body comes to rest
e) the distance fallen when the body comes to rest

I have managed to answer, a, b and c, but I would be really grateful if anyone could explain how to work out d and e since I have an exam tomorrow. Thanks, any help is appreciated.
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