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Thread ID: 57767	2005-05-12 06:22:00	Badly need help on my Algebra test	Renmoo (66)	PC World Chat

Post ID	Timestamp	Content	User
354351	2005-05-12 06:22:00	Greetings PressF1, recently I've got back my Maths test, in which I scored a "Merit" . (To Ninja, this has nothing to do with my homework!) However, I am badly unsatisfied with the Excellent question . This is what it says: Tara recently tried parachuting . After she jumped from the plane, she took 90 seconds to travel 4373m vertically downwards, then her parachute opened . During this 90 seconds of "free-fall", Tara initially accelerated due to gravity . Distance during the first section of free-fall is given by the equation: S=4 . 9t, in which S is the distance covered, while t is the time taken Then she reaced terminal velocity of 50 m/s Distance during the second section of free-fall is given by the equation: D=50m, in which D is the distance covered in the 2nd section and m is the time taken for the second section . The question: How long did it take Tara to reach terminal velocity? Can someone use a image-manipulation program or simple image-illustration program such as Microsoft Paint to draw out the situation? Thanks for reading this . Thank you very much . Cheers :)	Renmoo (66)
354352	2005-05-12 06:49:00	Tara recently tried parachuting. After she jumped from the plane, she took 90 seconds to travel 4373m vertically downwards, then her parachute opened. During this 90 seconds of "free-fall", Tara initially accelerated due to gravity. Distance during the first section of free-fall is given by the equation: S=4.9t, in which S is the distance covered, while t is the time taken Then she reaced terminal velocity of 50 m/s Distance during the second section of free-fall is given by the equation: D=50m, in which D is the distance covered in the 2nd section and m is the time taken for the second section. The question: How long did it take Tara to reach terminal velocity? Can someone use a image-manipulation program or simple image-illustration program such as Microsoft Paint to draw out the situation? Thanks for reading this. Thank you very much. Cheers :) Using simultaneous equations to find m, the time taken after terminal velocity is reached (1) 4.9t + 50m = 4373 (2) t + m = 90 (1) 4.9t + 50m = 4373 (2) 4.9t + 4.9m = 441 45.1m = 3932 m = 87.18.... Finding t, the time beofre terminal velocity is reached, from m Now that we have m, the time taken for the second section - we just subtact it from 90 seconds (the total time of free-fall) to get an answer of 2.82 seconds of inital free-fall before reaching terminal velocity. Or we can resubstitute to get: 4.9t + 50(87.18) = 4373 4.9t + 4359 = 4373 4.9t = 14 t = 2.86 seconds So the two methods are only a fraction of a second away from each other, indicating that the answer is right. Hope this helps, even though I didn't give you a diagram :)	george12 (7)
354353	2005-05-12 07:13:00	james, this (http://www.studyit.org.nz/) site is for you. its a NZ NCEA help site.there are real maths and science teachers that post very often. they cover biology, chem, maths, science and physics. some of the stufff there is pretty useful.	Prescott (11)
354354	2005-05-12 07:13:00	I specifically ask for a diagram that can show me what's happening in the question. If I know the situation, I can easily solve the question. Anyway, thanks for the solution, George Cheers :)	Renmoo (66)
354355	2005-05-12 09:08:00	I also did this question to amuse myself, my answer being only slightly different to George's. I will provide a diagram though, because I simply am not bothered to study for that Physics internal first period tomorrow. Admittedly that question is horrible to understand, but once you wade through the obligatory NCEA **** you'll see it's quite simple. Total time = 90 seconds. Therefore first section + second section = total time = 90 seconds. Simultaneous equations must be used, again :) t + m = 90 d + s = 4373 s = 4.9t d = 50m Shall we continue? m + t = 90 50m + 4.9t = 4373 50m + 50t = 4500 50m + 4.9t = 4373 ------------------ 0m + 45.1t = 4283 t = 4283 / 45.1 t = 2.78 seconds. ... and that's it. That means that the time taken to reach terminal velocity is infact 2.78 seconds. You can check this ofcourse: if he travels at 50m/s for ( 90 - 2.78 = ) 87.22 seconds, he will travel ( 87.22 x 50 ) = 4361m after reaching terminal velocity. 50(90-2.78) + 4.9(2.78) = 4374.622 (close enough) And here's the key ... well there would be a picture here if we could either use IMG code or upload attachements.	Growly (6)
354356	2005-05-12 09:15:00	Wow. I admire people who can speak maths. :confused:	pctek (84)
354357	2005-05-12 09:17:00	Sorry Jameskan, I just thought it might help. I'll can't really show speeds and times in a comprehensible way on a diagram :(	george12 (7)
354358	2005-05-12 10:56:00	To Growly, there is something called ImageF1. Ask sal about it, he is the admin.	Renmoo (66)
354359	2005-05-12 10:59:00	This is what I thought what is happening: Tara jumps down from the plane, she then free-falls for 4373m. After 90 seconds, in which she completes her 4373m, she achieved terminal velocity. In my opinion, the answer should be 90 seconds! We shouldn't be doing any maths at all! That's why I hope someone would be kind enough to draw a diagram and post it online. In the end, I wrote 90 seconds, which I got it wrong, no doubt.... Cheers :)	Renmoo (66)
354360	2005-05-12 11:13:00	This is what I thought what is happening: Tara jumps down from the plane, she then free-falls for 4373m . After 90 seconds, in which she completes her 4373m, she achieved terminal velocity . Therein lies your problem James, you don't know/understand what terminal velocity is, therefore you cannot understand or visualise the problem . You have assumed that Tara will continue to accelerate as she falls until her parachute opens . However, in reality after a very short period she will cease to accelerate as wind resistance equals gravitational force . (Or words to that effect, I'm neither a mathematician nor a physicist) . Perhaps a quick Google on terminal velocity might clear your head? Cheers Billy 8-{)	Billy T (70)
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