heyy, i have question abt position-time graph, i cant draw it so i'll try to explain it, it looks like an upside prabola, and the question asks first for the average velocity in certain time interval; i knew how to do that by subtracting xf-xi/tf-ti. but then another branch of te question is to determine the instantaneous velocity at t=2 by measuring the slope of the tangent ??? how do u find the slope at a certain second ?? and another brach is at what value of t is the velocity zero ??