Algebra Problem

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Created: 2011/12/31, Members: 42, Messages: 22740

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Anni313 Posts: 1,790 Joined: 2004/03/04	2005/02/14, 08:57 PM Okay, I totally give up. A person throws a rock upward from the edge of an 80-foot cliff. The height, H, in feet, of the rock above the water at the bottom of the cliff after x seconds is described by the function. H(x)=-16(x squared) + 64x + 80 a)what is the height of the rock after 3 seconds? I came up with 128 feet b)After how many seconds will the rock be at it's highest, and what will that height be? c)How long will it take the rock to reach the water. Hint the height would be 0) You may use the quadratic formula or the factoring technique. Well that's just hunky dory. Why are we throwin rocks anyway? What if we put somebody's eye out? Sigh.... -------------- Anni ******* In my head, I am out of my mind....

Pritchard Posts: 1,212 Joined: 2004/03/02	2005/02/15, 06:04 AM i dont know \|: -------------- wax on, wax off
asimmer Posts: 8,201 Joined: 2003/01/07	2005/02/15, 07:28 AM And how does this apply to anything in real life? i don't get why we want to know anything other than where not to stand when the rock comes back down... -------------- Vision without action is a daydream, Action without vision is a nightmare. -- Japanese Proverb --
Pritchard Posts: 1,212 Joined: 2004/03/02	2005/02/15, 07:31 AM anyway, people in glass houses shouldnt throw stones! (i have no idea how it relates the problem, but i wanted to use it!) -------------- wax on, wax off
jonathanweaver Posts: 576 Joined: 2004/06/14	2005/02/15, 11:16 AM Using the quadratic formula, I got that when H(x)=0, x=5 or -1. Since we are talking about time, I'd have to go with the 5. However, I'm questioning my answer based on the fact that after 3 seconds it was up at 128 feet, which I agree with. It's very possible that it would only take 2 seconds to fall that distance, since throwing the rock up has several negative factors: initial inertia, gravity, arm strength, natural arc. I'll try to figure out the "b" portion of the problem next. -------------- --Click here to insert a clever message-- Jonathan
goodoldtex Posts: 564 Joined: 2004/01/25	2005/02/15, 11:26 AM anni, the easiest way to find the maximum (if you have a graphing calculator ex: TI 83+) is to go into your graph (y=) and put the equation in the first y. hit graph. zoom fit. you'll have to press 2nd then calculate and go to maximum. it will tell you the height (y) and the seconds (x) i'm assuming the quadratic formula is correct...so i assume the -16x^2 is the force of gravity, because i remember it is -9.8m/s(squared)...but i do not remember the force of gravity in feet. If you have it all correct plug it into the quad form and you'll come out perfectly sorry i cannot give you a real answer, i leant my graphing calculator to my girlfriend for the semester since i am not taking any math courses.....i hope i helped some.
hecdarec Posts: 2,457 Joined: 2003/12/16	2005/02/15, 12:37 PM Is this a required course? I pray that I never have to do anything like this in my life. -------------- I skip faster than most people can run.
jonathanweaver Posts: 576 Joined: 2004/06/14	2005/02/15, 08:34 PM Ok. And here's the rest of it. Enjoy... H(x)=-16(x squared) + 64x + 80 a)what is the height of the rock after 3 seconds? I came up with 128 feet -169 + 643 + 80 = -144 + 192 + 80 = 48 + 80 = 128 correct b) after how many seconds will the rock be at it's highest, and what will that height be? rock will be at highest when v=0. Velocity = h'(x) Velocity = (-16(x squared) + 64x + 80)' Velocity = -32x + 64 V = 0 at x=2 Height = -64 + 128 + 80 = 144 c)How long will it take the rock to reach the water. Hint the height would be 0) You may use the quadratic formula or the factoring technique. H(x) = 0 = -16(x squared) + 64x + 80 div by 16 0 = -x squared + 4x + 5 x squared = 4x + 5 x = 5 (or -1, but that doesn't fit the word problem) -------------- --Click here to insert a clever message-- Jonathan
Anni313 Posts: 1,790 Joined: 2004/03/04	2005/02/15, 08:38 PM Jonathan you are THE best! That's what I came up with after I got done agonizing over why I was being made to this. -------------- Anni ******* In my head, I am out of my mind....
Anni313 Posts: 1,790 Joined: 2004/03/04	2005/02/15, 08:46 PM Jonathan! Check your email! -------------- Anni ******* In my head, I am out of my mind....
jonathanweaver Posts: 576 Joined: 2004/06/14	2005/02/16, 10:21 AM No problem, Anni. I LOVE Algebra!!! My wife thinks I should teach lower lever Algebra in college. I would teach up through College Algebra. After that, it starts getting difficult. LOL When I was in high school, my cousin, a CS major in college at the time, told me, "I have already forgotten more math than you've learned." I was able to tell my sister-in-law that the other night while helping her with her high school Algebra teacher. For fun, I bought "The Mensa Puzzle Calendar". I get all the math ones right, and most of the word ones wrong. I even found a mistake on one of the math questions. I had a friend double-check it, and he agreed with me. Bring on the Algebra problems... -------------- --Click here to insert a clever message-- Jonathan
nerraw Posts: 236 Joined: 2003/03/09	2005/02/16, 10:58 AM And you posted that on Valentines day too!
Anni313 Posts: 1,790 Joined: 2004/03/04	2005/02/16, 06:52 PM I really appreciate your help Jonathan. I have tremendous respect for people who understand algebra because I absolutely do NOT get it. -------------- Anni ******* In my head, I am out of my mind....
7707mutt Posts: 7,686 Joined: 2002/06/18	2005/02/16, 06:59 PM You math Nerds LOL that gave me a headache! -------------- If you can itch your nose after arm day...do another set! 7707mutt@freetrainers.com
jonathanweaver Posts: 576 Joined: 2004/06/14	2005/02/17, 12:15 PM I'd trade half of my math skills for half of your muscle mass, Mutt. I tell my wife stuff like that. I'd trade half my metabolism and energy for half of her muscle and fat mass. (I can burn off the fat, she can't.) -------------- --Click here to insert a clever message-- Jonathan
jonathanweaver Posts: 576 Joined: 2004/06/14	2005/02/18, 01:23 PM Ok. At a beauty parlor one busy Saturday, the staff found that there were 10 blondes. One-fourth of the customers were redheads, and half were brunettes. How many customers altogether? -------------- --Click here to insert a clever message-- Jonathan
hecdarec Posts: 2,457 Joined: 2003/12/16	2005/02/18, 01:25 PM 10 -------------- I was 17 years old the first time my father told me he loved me.
jonathanweaver Posts: 576 Joined: 2004/06/14	2005/02/18, 01:31 PM Nope. There we 10 blondes. There were also some redheads and brunettes in there as well. Good guess though. :-) I figured DFly would enjoy this one... -------------- --Click here to insert a clever message-- Jonathan
howdiekat Posts: 1,345 Joined: 2003/05/22	2005/02/18, 01:33 PM 40 -------------- if you get me started on quentin tarantino films, chances are you won't be able to shut me up. excuses are really good for making you fat. margarine is a liar who announces, "i am butter!"
hecdarec Posts: 2,457 Joined: 2003/12/16	2005/02/18, 01:45 PM 40 -------------- I was 17 years old the first time my father told me he loved me.
jonathanweaver Posts: 576 Joined: 2004/06/14	2005/02/18, 03:04 PM Yup. -------------- --Click here to insert a clever message-- Jonathan
Carivan Posts: 8,542 Joined: 2002/01/20	2005/02/18, 03:30 PM 40? -------------- Scales are for dead weight: We are not dead yet! Still trying to find out how to do the Hollywood Free Press. Ivan carivan@freetrainers.com Montreal Canada
hecdarec Posts: 2,457 Joined: 2003/12/16	2005/02/18, 04:53 PM Carivan if you cannot understand the answer I am not going to waste my time explaining it to you. -------------- I was 17 years old the first time my father told me he loved me.
Carivan Posts: 8,542 Joined: 2002/01/20	2005/02/18, 05:30 PM C'mon Hec, explain it to me! -------------- Scales are for dead weight: We are not dead yet! Still trying to find out how to do the Hollywood Free Press. Ivan carivan@freetrainers.com Montreal Canada