To calculate the time until an object hits the ground when thrown upwards off a cliff, use the equation d = vt + 1/2(at^2), where d is the height of the cliff (considered a negative value), v is the initial velocity, and a is the acceleration due to gravity (-9.8 m/s²). The object first moves upwards until its velocity reaches zero, then descends back down, passing the initial throw point. The total vertical displacement to consider is the height of the cliff, as you are ultimately solving for when the object reaches the ground. The quadratic formula can be utilized to find the time, as the upward and downward movements are accounted for in the displacement. This method effectively combines both the upward motion and the downward fall to determine the total time until impact.