When an object is thrown upward, its height (s), in meters, is given (approximately) by the quadratic equation s= -5t^2+vt+h, where v is the upward initial velocity in meters/seconds, t is the time of flight in seconds, and h is the height above level ground from which the object is thrown. johnny is standing on a platform 10 meters high and throws a ball straight up as high as he can at a velocity of 23 meters/second. at what time t will the ball hit the ground