Change in speed = (end speed) - (start speed)
= (22 m/s) - (4 m/s) = 18 m/s .
Magnitude of average acceleration =
(change in speed) / (time for the change) .
= (18 m/s) / (3 sec) = 6 m/s² .
That's about 0.61 G.
If you weigh 150 pounds, then you would feel as if there's
a force of 92 pounds pushing you back against the seat !