Question

A skateboarder has an acceleration of −1.9 m/s2. If her initial speed is 6 m/s, how long does it take her to stop?

Answer 1

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.