## 9 pm, and still dont understand

1. The problem statement, all variables and given/known data
A rifle bullet is fired at an angle of 30 degrees below the horizontal with an initial velocity of 800 m/s from the top of a cliff 80 m high. How far from the base of the cliff does it strike the level of ground below
g=9.8
initial velocity- 800 m/s
y=80 m

2. Relevant equations
R=(initial velocity squared x sin(2 theta)
g

3. The attempt at a solution
i did
800^2 x sin2(30)
9.8

i get 56556.76106-which seems way to high
Then i did Soh Cah Toa
56556.76106/80
and got 706.9595133

I really just dont understand what i am doing, and need help. bad. this is due tomorrow.
 Hello welcome to Physicsforums! Hope you will learn here and also teach us what you know! For the problem: (1)You must resolve the initial velocity into their X and Y coordinates using trigonometry. (2)Then use kinematic equations to solve the problem.
 I dont even know any of that. We never learned Kinematic equations. Im very slow at this, and am now regretting taking this class.

## 9 pm, and still dont understand

Hey don't despair! I can teach you what I know. I am learning this myself.

Kinematic Equations:
S=Vot+0.5at^2
S=Vft-0.5at^2
S=((Vo+Vf)/2)*t
Vf=Vo + at
Vf^2=Vo^2 + 2aS

S=Displacement in metres
Vo=Initial Velocity in metres/second
Vf=Final Velocity in metres/second
a=acceleration in metres/second squared
t=time in seconds

For all kinematic problems, write your 5 variables down and write the known values in.

Velocity is a vector quantity. It has magnitude and DIRECTION. direction is usually indicated by an angle as in your problem.

Velocity of the bullet is 800m/s angle 30degrees below the horizontal. Draw a picture and see if you can resolve the velocity into X and Y coordinates.

Have a look at this site:
http://www.glenbrook.k12.il.us/gbssc...ors/u3l2c.html

Then we will see if we can solve the problem. Please come back.

 Quote by megg0230 I dont even know any of that. We never learned Kinematic equations. Im very slow at this, and am now regretting taking this class.
 Here is a better site. http://id.mind.net/~zona/mstm/physic...lSolution.html
 use the 2nd equation to find time keep in mind the bullet is being fired DOWN, so your y value must be negative when you find time, disregard the negative value then use the 1st equation to find x