For the sake of explaining it easily, let\'s use this question: A projectile is

Question

For the sake of explaining it easily, let's use this question:

A projectile is fired with an initial speed of 120m/s at an angle of 55 degrees above the horizontal axis from the top of a 50m high cliff. Find the time it takes to reach the base of the cliff.

I did it like this:

4.905t^2+98.3t-542.5=0

Note: I did not actually round here, but this is where I get stuck every time. The textbook I pulled this question from says the total time is 20.5 seconds, but I cannot get past this step. I would really like to know what I'm doing wrong or where I am supposed to go from here with this question. I know this is really long and there are probably more important questions for you to answer, but thank you for helping me anyways.

Explanation / Answer

So, I found a small part that needs to be corrected. In the formula d = vit + (1/2)at^2 d = y2 - y1 y2 = 0 because the object reached the ground y1 = 542.5 because this is the initial height the object was at. d = 0 - 542.5 Also, a = g (gravity) which you know is 9.81 If you imagine a y-axis, as the arrow moves up, y value is positive. The object is accelerating Downward, so y value is negative, a = -g. a = -9.81 The formula looks like this now, -542.5 = 98.3(t) + (1/2)(-9.81)t^2 0 = -4.905t^2 + 98.3t + 542.5 t = 24.5s I know this is not the exact answer in your book, but I hope this helped steer you in the right direction to get 20.5s.

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