Very Last Question 2009 Exam 2

[genetek995]

Hey guys, I just finished the 2009 VCAA Exam 2. For the last question, I typed the integral correctly into my cas only to get -3.4 instead of 254 seconds. Is anyone else having this problem? I'm 100% sure I typed into my cas correctly.

[A-i-d-a-n-K]

Yep got this exact same issue with TI-89, even when I defined t>0 it just said 'false'.

I ended up subbing in random values of t till I found one that gave 1200 as a solution, but that took a while so hopefully the calculator can handle anything VCAA throws at us this year!

[genetek995]

OMG I swear, if my CAS plays up on the day. I'm going to sue Texas Instruments...

[acinod]

Hey I just did this too but I use a TI-nspire CAS.

Typed in solve(1200=integral from t to 0 (9.8/2*(1-e^-2x))dx,t)|t>0 and I got t=245.393 but it says 'More solutions may exist'.

If it's a problem with your calculator brand then VCAA might let it go, but they can always come up with stuff like you should have downloaded the latest version or crap like that.

[genetek995]

Thanks Tony Tam. Yeah, did that too oh well. Good luck for tomorrow guys.

[Zebra]

If i remember correctly, my TI nspire (Cas) told me FALSE.

Now, if this happened in this year exam what would happen?

[Asx4Life]

Cant we use triangles for this question? Like find the horizontal distance and vertical distance, then pythagoras it?

[A-i-d-a-n-K]

Cant we use triangles for this question? Like find the horizontal distance and vertical distance, then pythagoras it?

Yeah the trouble was to find the horizontal distance you needed to know the time, hence had to solve(1200=integral from t to 0 (9.8/2*(1-e^-2x))dx,t)|t>0 which gave the wrong solution on CAS.

[Zebra]

mm if this happens im will fkn sue VCAA just like helen

[ellecee]

My Ti-89 also failed to give me an answer when solving for the time.
If such a situation comes up during the exam, don't forget GRAPHS! Put y1=equation, y2=1200, find intersection, and voila! The answer appears.

[DannyN]

Cant we use triangles for this question? Like find the horizontal distance and vertical distance, then pythagoras it?

Yeah the trouble was to find the horizontal distance you needed to know the time, hence had to solve(1200=integral from t to 0 (9.8/2*(1-e^-2x))dx,t)|t>0 which gave the wrong solution on CAS.

you can find t by hand, like antidif 9.8/2*(1-e^-2x))dx  given that when t=0, x=0 and find an equation in terms of x then solve when x 1200, and you'll get your time

[funkyducky]

My ti-89 gave me -3.4 too. Solution - I graphed y1=4.9(1/2e^(-2x)+x-1/2) and y2=1200 and found the intersection @ x=245.39...