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# SUVAT questions. Watch

1. I'm having trouble understanding the whole projectiles thing.

Is g always -9.81 if you consider upwards as positive and downwards as negative?

If a projectile is thrown horizontally it's just distance/time to find its speed, but if it's thrown at an angle like a javelin is it Fcosx or Fsinx... and even then what have you found?

Argh!
2. Yes gravity is always that.

The projectile...you can make a triangle (right-angled)

and then to find the speed it would be the hypotenuse, and depending on whether you had the vertical or horizontal it would be cos or sin
3. So when resolving the vertical component it's always time and when resolving the horizontal component it's always distance?
4. Gravity is negative if you take downwards acceleration to be positive which is the way most people think of it.

Resolve your velocity into it's horizantal and vertical components, by using trigonometry.

Then you only need consider the vertical component for how long it's in the air since the horizantal component is not affected by acceleration.

Just practice some questions.
5. (Original post by Vicious Fishes)
So when resolving the vertical component it's always time and when resolving the horizontal component it's always distance?
In a way yes. But remember it is also travelling a distance vertically. But if it comes back to the same height it was at originally it's vertical displacement is 0 yet it's horizantal displacement may be greater than or equal to 0 (depends what angle it was thrown at).
6. I think I get it now.

Thanks.
7. (Original post by Vicious Fishes)
I think I get it now.

Thanks.
Seriously just go and do a few questions, and then it will make sure it sticks
8. (Original post by Jooeee)
Gravity is negative if you take downwards acceleration to be positive which is the way most people think of it.

Resolve your velocity into it's horizantal and vertical components, by using trigonometry.

Then you only need consider the vertical component for how long it's in the air since the horizantal component is not affected by acceleration.

Just practice some questions.
will g always be negative because some books show both. How much impact would it have on the answer.

Also how do you know if you need to use horizontal or vertical?

Updated: May 28, 2009
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