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Need help solving this formula problem?
Original problem: The height h(in feet) of an object that is dropped from the height of s feet is given by the formula h= s -16t^2, where t is the time the object has been falling. A 5 foot tall woman on a sidewalk looks directly overhead and sees a window was her drop a both from the 5 story (literally what the problem says). How long does she have to get out of the way? Round to the nearest tenth. (A story is 12 feet). Choose the answer from the following:
1.9 sec
2.4 sec
2.0 sec
2.1 sec
I was told by a math tutor to multiply the 5 feet by 12 feet to get the number of stories. And then subtract by the 5 feet to get the actual number of feet and plug it into the formula h = 60 - 16t^2. But when I do that, I don't get any of the answers. So I am very confused where to proceed from here. Help would be greatly appreciated.
2 Answers
- Marc MLv 71 decade agoFavorite Answer
First, calculate the total height of the building: 5 stories * 12 ft / story = 60 ft up, assuming that the "both" (whatever that is) is dropped from the top of the 5th story. So, s is 60.
We also must assume that the "both" would strike the woman in the head (of course, it could also hit a foot, a knee, etc., but more on this below), so the final height of the object h is 5.
So, if you subtract 60 from both sides, you come up with -55 = -16t^2, and t^2 = 3.4375. So, t = 1.85. Rounded up, this gives 1.9 sec.
Alternately, if the "both" hit her foot, knee, ankle, etc., it would take longer (but not much more so). Assume h = 0. Then, subtract 60 from both sides to get -60 = -16t^2, and t^2 = 3.75. Therefore, t = 1.93. Rounded down, this still gives 1.9 sec.
1.9 sec. is your answer.
Source(s): http://en.wikipedia.org/wiki/Standard_gravity http://en.wikipedia.org/wiki/Equations_for_a_falli... - 1 decade ago
there is a major issue. We dont know what h is.
Their are two variable so the question is unable to be solved. The closest answer is t=-sqrt((-h+55)/16) which is simply a different way of writing it.
Ask you teacher how tall the object is.
Its a strange question.
By the way what grade is this?
