A ball is projected upward with initial velocity = 20 m/s.
I have to show that the acceleration at time t is a(t)i, in which
a(t) = -g/b^2 * (v(t)^2 + b^2),
where v(t)i is the velocity of the ball at time t, and b^2 = mg/0.2D^2.
I'm taking a course that is kind of just quickly breezing through simple mechanics, but it's insufficiently explained and i find my tutor unhelpful.
Can somebody explain what exactly is being asked here and... nudge me in the right direction.