physics
posted by kevin .
i.imgur . com/jXIYL. png
is it 20 and 10??

between 1 and 2 seconds the distance covered is +20
so 20 m/s Yes
between 2 and 4 seconds the distance is 20 so velocity is 20/2 = 10 m/s
You missed the negative sign, the slope is down at three seconds