[Video] Q25: H = -4.9t^2 + 25t the equation above expresses the approximate height h, in meters, of a ball t seconds after it is launched vertically upward from the ground with an initial velocity of 25 meters per second. after approximately how many seconds will the ball hit the ground?

Explanation for Question 25 From the Math (Calc) Section on the Official Sat Practice Test 1

Now question number 25 shows us the equation above that represents the approximate height, 2 H of a ball T seconds. After it's launched upward from the ground with 3 an initial velocity of 25 meters per second. 4 And they want to know after approximately how many seconds will the ball hit 5 the ground. Right? So if the ball is hitting the ground, 6 we're starting here, maybe on the ground, 7 right? Yeah. It's launched from the ground and then we want it to go 8 up and we want it to hit the ground again. 9 So we can ask ourselves, what is the height when the ball is on 10 the ground? And if the height, 11 or I guess if we're on the ground, right? Our height has to be 12 equal to zero because we have no, 13 we have no height to support us. We're just simply sitting on the baseline 14 and the baseline is going to be zero. 15 So if we want to know, when the ball hits the ground, we need 16 to set our height is equal to zero. And then from there we can 17 fill in the blanks here, 18 right? And we're trying to solve for T after how many seconds. 19 So we're trying to solve for T. Now we can take this equation here. 20 4.9 T squared plus 25 T and solve for T first 21 by factoring out a T, right. We can say T negative four point 22 19 plus 25, because both of these terms have a T in them. 23 And so now I just want to set both of these equal to zero 24 so I can solve for them. It's kind of just like normal factoring with 25 an X, but instead we're going to use a T, right? 26 So here's...