At which time(S) does the firework momentarily stop?

Question

the position of a firework as it flies is given by the function s(t)=10+50t-0.8t^2

Answer 1

It stops instantaneously when its speed is zero.

 

v = ds/dt = 50 - 1.6t = 0 ⇒

 

t = 50/1.6 sec = 31.25 sec (assuming the time units are seconds)