Question 395288
Note that t = 2 is fairly close to the vertex which occurs at {{{t = 20/-9.8 = 2.041}}} seconds. Therefore the velocity is close to 0 m/s.


To determine an exact value, if we have {{{X = -4.9t^2 + 20t + 15}}}, then {{{dX/dt = -9.8t + 20}}}, and the velocity at time t = 2 is {{{dX/dt = -9.8(2) + 20 = .4}}} m/s, so the rate of change in height is .4 meters per second (upward since positive numbers are chosen to represent upward for this particular problem).