checking if correct

zee-f · 2011-08-04 01:25:00

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

#18- 117.6=24.5+ t o.5 * 9.8t^2

4.9t^2+ 24.5t-117.6=0

19. Solve the equation you chose in question 18 to determine when the ball will hit the ground. (HINT: If you don't get one of the answers listed for this question, then maybe you chose the wrong equation in #18. Use this opportunity to double check your work!)

t = 8 seconds
t = 4 seconds
t = 3 seconds
t = -3 seconds
The ball will never reach the ground.

19- t=3 seconds

4.9*9+24.5*3-117.6=0

20. Using the same equation, determine when the ball is at a height of 49 meters.

(confused)

bobbym · 2011-08-04 01:35:36

Hi;

t2 is a variable. Please correct and write that as t^2. That is the proper way. Please do that now.

zee-f · 2011-08-04 01:39:37

4.9t^2 + 24.5t + 117.6 = 0
-4.9t^2 - 24.5t + 117.6 = 0
-4.9t^2 + 24.5t - 117.6 = 0
4.9t^2 + 24.5t - 117.6 = 0
-4.9t^2 + 24.5t + 117.6 = 0

my bad i missed that

bobbym · 2011-08-04 02:22:28

Hi;

What did you get? How did you work it?

zee-f · 2011-08-04 02:27:23

am getting 4.9t^2+ 24.5t-117.6=0

S = ut + 0.5at² S = dist, u = initial velocity, t = time a = acc due to gravity

117.6 = 24.5t + 0.5 x 9.8 t²

4.9t² + 24.5t - 117.6 = 0

bobbym · 2011-08-04 02:28:50

Is not gravity a force that acts downward towards the ground?

zee-f · 2011-08-04 06:30:15

18. -4.9t2 + 24.5t + 117.6 = 0

19. -4.9 (t - 8) (t + 3) = 0
t = 8 second

bobbym · 2011-08-04 06:47:05

In which direction is the ball thrown? Up, down or horizontally?

zee-f · 2011-08-04 06:53:20

up

bobbym · 2011-08-04 06:55:06

Your sure?

zee-f · 2011-08-04 07:00:58

no my bad down because its going above the ground

bobbym · 2011-08-04 07:06:01

Yes, that is what I have in my notes.

Now you must re solve the problem. I get:

Of course we can move everything over to the other side and get:

zee-f · 2011-08-04 07:55:34

i will need to use the formula 4.9t2 + v0t = s, where t is the time in seconds, v0 is the initial velocity, and s is the distance in meters. Approximately how far will an obj

bobbym · 2011-08-04 07:56:40

That is my second formula above your post, can you solve it?

anonimnystefy · 2011-08-04 07:58:43

have you done the second problem?

zee-f · 2011-08-04 08:10:02

t = {3, -8}

bobbym · 2011-08-04 08:11:18

That is correct for the first one. That means the ball will hit the grounbd in 3 seconds. You disregard the negative answer.

zee-f · 2011-08-04 08:17:43

i said that previously lol that t=3 the only confusing one is number 20

bobbym · 2011-08-04 08:24:24

Set the right hand side to 49 instead of 0 in the top equation.

anonimnystefy · 2011-08-04 08:24:47

look at the distance as the difference of th total height and the given height which is 117,6-49=68,6.everything else stays the same.

zee-f · 2011-08-04 08:24:59

do i change 117.6 meters to 49

bobbym · 2011-08-04 08:25:41

No, read the above posts!

zee-f · 2011-08-04 08:25:59

i typed that before i saw ur earlier post anonimnystefy sorry

bobbym · 2011-08-04 08:28:46

Or look at post #49 it is all done for you, just solve it.

zee-f · 2011-08-04 08:31:16

post 49 ????

Math Is Fun Forum

#1 2011-08-04 01:25:00

checking if correct

#2 2011-08-04 01:35:36

Re: checking if correct

#3 2011-08-04 01:39:37

Re: checking if correct

#4 2011-08-04 02:22:28

Re: checking if correct

#5 2011-08-04 02:27:23

Re: checking if correct

#6 2011-08-04 02:28:50

Re: checking if correct

#7 2011-08-04 06:30:15

Re: checking if correct

#8 2011-08-04 06:47:05

Re: checking if correct

#9 2011-08-04 06:53:20

Re: checking if correct

#10 2011-08-04 06:55:06

Re: checking if correct

#11 2011-08-04 07:00:58

Re: checking if correct

#12 2011-08-04 07:06:01

Re: checking if correct

#13 2011-08-04 07:55:34

Re: checking if correct

#14 2011-08-04 07:56:40

Re: checking if correct

#15 2011-08-04 07:58:43

Re: checking if correct

#16 2011-08-04 08:10:02

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#17 2011-08-04 08:11:18

Re: checking if correct

#18 2011-08-04 08:17:43

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#19 2011-08-04 08:24:24

Re: checking if correct

#20 2011-08-04 08:24:47

Re: checking if correct

#21 2011-08-04 08:24:59

Re: checking if correct

#22 2011-08-04 08:25:41

Re: checking if correct

#23 2011-08-04 08:25:59

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#25 2011-08-04 08:31:16

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