Questions about finding position, velocity, acceleration related

1. Feb 27, 2013

Ryukouki

A stone is thrown upward from the top of a 20 m high cliff at an angle of 25 degrees. The stone has an initial velocity of 15 m/s. Make the BASE of the cliff the origin. (a) Write out the position, velocity, and acceleration vectors for the stone. (b) What is the magnitude of the velocity of the stone 3 s after it is launched?

I can understand what is being asked, but not exactly sure on how to reach the answer. I feel like it has do do with finding the components V(0)x and V(0)y with the V(0)cos(θ) and V(0)sin(θ) functions...

Thank you so much in advance! :)

EDIT: Main formulas:

Three key variables (displacement, time, velocity) lead to three key relationships relating each pair:

velocity & time:
v=v0+at

displacement & time:
x=x0+v0t+(1/2)at^2

velocity & displacement:
v2=v^20+2aΔx

2. Feb 27, 2013

Staff: Mentor

Re: Questions about finding position, velocity, acceleration related..

Did you draw a sketch?
What is the initial position of the stone?
You know the velocity and its direction - can you calculate the horizontal and vertical components of this velocity?

3. Feb 27, 2013

Ryukouki

Re: Questions about finding position, velocity, acceleration related..

1. Yeah I drew a sketch, a rather ugly ugly sketch. :(
2. The initial position of the stone... how exactly do you find that? Wait, that's not V0 is it? EDIT: Wait, wait. The initial position of the stone, since the cliff is 20 m high, would be at the coordinates (0,20) then, correct?
3. Velocity is 15 m/s, and the direction is 25 degrees. Correct? So, with THAT information, correct or not, am I to try and find the components using the angle and its respective sin and cosine properties?

Am I on the right track so far? Sorry! I'm a chemistry student, and this is my first ever physics class. >_>

4. Feb 27, 2013

Staff: Mentor

Re: Questions about finding position, velocity, acceleration related..

Right
That is given in the problem statement, indeed.
That is a good idea.

5. Feb 27, 2013

Ryukouki

Re: Questions about finding position, velocity, acceleration related..

Thanks for your help thus far! So lemme ask this, do I also need to calculate the magnitude of the initial position yet? What exactly do I do with that initial position? I have the components.

6. Feb 28, 2013

Staff: Mentor

Re: Questions about finding position, velocity, acceleration related..

You just have to find the initial position, it is not relevant for the other parts of the problem.

7. Feb 28, 2013

Ryukouki

Re: Questions about finding position, velocity, acceleration related..

Yeah, I got it after like three hours pondering it. :P Finished the whole problem.