Physics
posted by Sasha on .
I found the first three parts of the question but I can't figure out part d.
The instruments attached to a weather balloon in the figure below have a mass(m) of 5.5 kg. The balloon is released and exerts an upward force(F) of 109 N on the instruments.
(a) What is the acceleration of the balloon and instruments?
10.02m/s^2
(b) After the balloon has accelerated for 10 s, the instruments are released. What is the velocity of the instruments at the moment of their release?
100.2 m/s
(c) What net force acts on the instruments after their release?
53.9N
(d) When does the direction of the instrument's velocity first become downward?
This is the one I can't figure out

direction of velocity is downward at maximum height, and net velocity is zero.
vf=0=vi+at=100.2m/sg*t
solve for t. This time is seconds after the acceleration of 10s 
I don't understand this formula?

these are the two answers I got...
10
or
10.22 
how did you get the first three answers?