Ok so we know:
The acceleration (10ms^-2)
The initial velocity (0)
And the total time (6seconds)
Using the equation v = u + at, with v being the final velocity, u being the initial velocity, a being acceleration and t being time, we get:
v = 0 + 10x6
v = 60
So the speed after 6 seconds is 60 metres per second (6m/s)
Hope this helped
