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# M1 Projectiles Watch

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1. If I don't get part A correct, I'm screwed for the rest of the questions.

Is it tan inverse 6/8 ?? ie 36.9 degrees? (3SF)

2. Where do you get the 8 from? Use toa.
3. (Original post by Hopple)
Where do you get the 8 from? Use toa.
So its tan inverse 6/10?

IDK but I put the velocity of 8 as part of the triangle then assumed 10 must have been the hyptonuse, so i thought 8 was the adjacent :|
4. (Original post by MSI_10)
So its tan inverse 6/10?
Yeah, that's it.
5. yes tanα is 6/10
6. (Original post by Hopple)
Yeah, that's it.
Aight thanks.

Am I starting part b probably; to get time, first need to use S. Do I use 6 or 10..?

Then SUVAT (S=ut+o.5at^2) use quadratic formula to get t?
7. (Original post by MSI_10)
Aight thanks.

Am I starting part b probably; to get time, first need to use S. Do I use 6 or 10..?

Then SUVAT (S=ut+o.5at^2) use quadratic formula to get t?
For part b, are you looking at vertical or horizontal motion (or both)? And yes, that suvat equation will do.
8. (Original post by Hopple)
For part b, are you looking at vertical or horizontal motion (or both)? And yes, that suvat equation will do.
I did this..
S=-6
a=-9.8
U=8sin31..

-6=8sin31t-4.9t^2
-4.9^2+8sin31t+6=0
got t=1.60 or t=-0.763

9. (Original post by MSI_10)
I did this..
S=-6
a=-9.8
U=8sin31..

-6=8sin31t-4.9t^2
-4.9^2+8sin31t+6=0
got t=1.60 or t=-0.763

Make sure you're measuring everything in the same direction.
10. (Original post by Hopple)
Make sure you're measuring everything in the same direction.
:\
11. (Original post by MSI_10)
:\
Even though everything's going downwards, you've made displacement and acceleration be in the opposite direction to initial velocity.
12. (Original post by Hopple)
Even though everything's going downwards, you've made displacement and acceleration be in the opposite direction to initial velocity.
Oh that's what you meant, yeah i get what you mean now thanks

So t=0.763
13. Hmm, can anyone check if im doing part c correctly.

It's asking for distance.. do I use the time obtained from part b, use S=ut+1/2at^2 but use 8cos31 for u instead of 8sin31..?
14. (Original post by MSI_10)
Hmm, can anyone check if im doing part c correctly.

It's asking for distance.. do I use the time obtained from part b, use S=ut+1/2at^2 but use 8cos31 for u instead of 8sin31..?
Yes, but remember there are no forces acting horizontally here.
15. (Original post by finality)
Yes, but remember there are no forces acting horizontally here.

Alright so I used 8sin31
I get the answer as 6m. Something tell's me this aint right; it seems to high :\

Updated: May 6, 2012
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