checking if correct

bobbym · 2011-08-04 08:32:29

Post # 19 , sorry!

I was thinking of the 49 meters.

zee-f · 2011-08-04 08:39:30

117.6 + -49 + -24.5t + -4.9t2 = 49 + -49

117.6 + -49 = 68.6
68.6 + -24.5t + -4.9t2 = 49 + -49

49 + -49 = 0
68.6 + -24.5t + -4.9t2 = 0

.
-14 + 5t + t2 = 0

-14 + 5t + 14 + t2 = 0 + 14

-14 + 14 + 5t + t2 = 0 + 14

-14 + 14 = 0
0 + 5t + t2 = 0 + 14
5t + t2 = 0 + 14

0 + 14 = 14
5t + t2 = 14

5t + 6.25 + t2 = 14 + 6.25

6.25 + 5t + t2 = 14 + 6.25

14 + 6.25 = 20.25
6.25 + 5t + t2 = 20.25

(t + 2.5)(t + 2.5) = 20.25

t + 2.5 = 4.5

2.5 + t = 4.5

2.5 + -2.5 + t = 4.5 + -2.5

2.5 + -2.5 = 0.0
0.0 + t = 4.5 + -2.5
t = 4.5 + -2.5

4.5 + -2.5 = 2
t = 2

bobbym · 2011-08-04 08:40:45

Correct! Very good!

zee-f · 2011-08-04 08:53:19

thanks to u

bobbym · 2011-08-04 08:54:09

You are welcome! See you tomorrow.

zee-f · 2011-08-06 01:49:20

for number 18 this is what my teacher said

#18. This equation is not correct. How do you know which terms are positive and which are negative?

bobbym · 2011-08-06 01:53:02

Please bring #18 down.

zee-f · 2011-08-06 02:09:23

18. A tennis ball is launched with an initial velocity of 24.5 m/s from the edge of a cliff that is 117.6 meters above the ground. Which quadratic equation could be used to correctly determine when the ball will hit the ground:

4.9t2 + 24.5t + 117.6 = 0
-4.9t2 - 24.5t + 117.6 = 0
-4.9t2 + 24.5t - 117.6 = 0
4.9t2 + 24.5t - 117.6 = 0
-4.9t2 + 24.5t + 117.6 = 0

bobbym · 2011-08-06 02:10:27

You told me that the ball was thrown downward at the ground. Is this how your teacher wants it?

zee-f · 2011-08-06 02:17:23

yup as the question says

bobbym · 2011-08-06 02:18:14

Well, which one did he/she say was correct?

zee-f · 2011-08-06 02:25:58

i have to find a new answer the incorrect one is the 4.9t^2 + 24.5t - 117.6 =0 one

bobbym · 2011-08-06 02:27:09

Is that what you picked? #2 and #4 are the same! In my opinion they are the correct answer.

zee-f · 2011-08-06 02:28:07

this is what i posted -4.9t^2 - 24.5t + 117.6 =0
move everything over to the other side and get:

4.9t^2 + 24.5t - 117.6 =0
this is what she said This equation is not correct. How do you know which terms are positive and which are negative?

bobbym · 2011-08-06 02:30:09

Gravity is downward so the 4.9t^2 is negative. The ball is thrown downward so 24.5t is negative also. The 117.6 is the height of the ball initially so it is positive. Your teacher is a boob!

zee-f · 2011-08-06 02:31:37

i knowwwwwwwwww its soooo annoying this makes me hate posting work to her i mean i totally dont get what i did wrong

bobbym · 2011-08-06 02:34:59

Ask your teacher how many seconds she thinks it will take for the ball to hit the ground? I very much would like to hear her answer.

zee-f · 2011-08-06 02:40:11

ok i willl ask her and illl explain to her my answer to ill tell you what happens when she answers thank you for allll your help bobbym i think am getting math allot more thanx to u and all ur help

bobbym · 2011-08-06 02:41:32

Please get her answer. I am really mad over it! I might recommend she come and visit here so she can learn something.

zee-f · 2011-08-08 06:41:51

hey bobbym this is her reply

#18. In the equation, the only thing that is negative is the gravity. The 24.5 is the velocity or speed, so it is not negative. Use -4.9t2 + 24.5t +117.6 = 0 to try number 19.

bobbym · 2011-08-08 06:44:39

Sorry, to show that the ball is being thrown downward, the 24.5t is negative.

With her equation it takes 8 seconds to hit the ground this is of course nonsense and I can prove it.

zee-f · 2011-08-08 06:57:48

so her equation is incorrect

bobbym · 2011-08-08 07:00:55

Yes, I am sure of that. Are you sure the ball is thrown downward?

anonimnystefy · 2011-08-08 07:01:36

http://www.kutasoftware.com/free.html

check out the 'quadratic functions' section.you can practise the problems.

zee-f · 2011-08-08 07:07:48

thank you anonimnystefy i will try them after i finish my lesson for today thanx alot

and bobbym this is what it says

A tennis ball is launched with an initial velocity of 24.5 m/s from the edge of a cliff that is 117.6 meters above the ground. Which quadratic equation could be used to correctly determine when the ball will hit the ground:

Math Is Fun Forum

#26 2011-08-04 08:32:29

Re: checking if correct

#27 2011-08-04 08:39:30

Re: checking if correct

#28 2011-08-04 08:40:45

Re: checking if correct

#29 2011-08-04 08:53:19

Re: checking if correct

#30 2011-08-04 08:54:09

Re: checking if correct

#31 2011-08-06 01:49:20

Re: checking if correct

#32 2011-08-06 01:53:02

Re: checking if correct

#33 2011-08-06 02:09:23

Re: checking if correct

#34 2011-08-06 02:10:27

Re: checking if correct

#35 2011-08-06 02:17:23

Re: checking if correct

#36 2011-08-06 02:18:14

Re: checking if correct

#37 2011-08-06 02:25:58

Re: checking if correct

#38 2011-08-06 02:27:09

Re: checking if correct

#39 2011-08-06 02:28:07

Re: checking if correct

#40 2011-08-06 02:30:09

Re: checking if correct

#41 2011-08-06 02:31:37

Re: checking if correct

#42 2011-08-06 02:34:59

Re: checking if correct

#43 2011-08-06 02:40:11

Re: checking if correct

#44 2011-08-06 02:41:32

Re: checking if correct

#45 2011-08-08 06:41:51

Re: checking if correct

#46 2011-08-08 06:44:39

Re: checking if correct

#47 2011-08-08 06:57:48

Re: checking if correct

#48 2011-08-08 07:00:55

Re: checking if correct

#49 2011-08-08 07:01:36

Re: checking if correct

#50 2011-08-08 07:07:48

Re: checking if correct

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