You said that she's losing 1.9 m/s of her speed every second.
So it'll take
(6 m/s) / (1.9 m/s²) = 3.158 seconds (rounded)
to lose all of her initial speed, and stop.
Answer:
The number of turns in secondary coil is 4000
Explanation:
Given:
Current in primary coil
A
Current in secondary coil
A
Number of turns in primary coil 
In case of transformer the relation between current and number of turns is given by,

For finding number of turns in secondary coil,



Therefore, the number of turns in secondary coil is 4000
Speed uses distance and velocity uses displacement in its calculation.
For 100 m race, distance = displacement. Hence speed = velocity
For 400m race, distance ≠ displacement. distance = 400m whereas displacement = 0m. Hence speed ≠ velocity