= - 9.8 The initial conditions are x (0) = 19.6 and v (0) = 0 So, v =
dx
dt
= - 9.8t + v(0) = - 9.8t ∴ x = -4.9 t2 + x (0) = - 4.9 t2 + 19.6 Now, the domain of the function is restricted since the ball hits the ground after a certain time. To find this time we set x = 0 and solve for t. 0 = - 4.9 t2 + 19.6 ⇒ t = 2