# Homework Help: Projectile Motion, Finding the Angle

1. Oct 6, 2009

### needlottahelp

1. The problem statement, all variables and given/known data
A projectile is fired in such a way that its horizontal range is equal to three times its maximum height. What is the angle of projection?

2. Relevant equations
Kinematics Equations

3. The attempt at a solution
I'm not even sure where to start. Can someone point me in the right direction?

2. Oct 6, 2009

### Delphi51

Lotta, as soon as you see the word "projectile", separate the initial velocity v at angle A into horizontal and vertical parts. Then write two headings:
Horizontal and Vertical. Decide in each case whether you have constant speed or accelerated motion and write the appropriate formula(s). Put in the numbers or expressions for all known quantities and look for an equation you can solve.

3. Oct 7, 2009

### needlottahelp

ok so I tried fitting the x and y components into various kinematics equations but I can't seem to isolate any variables to find the angle
I get things like
19.6h = Vy^2
or 3h = Vx t
any hints?

4. Oct 7, 2009

### Staff: Mentor

Write out the traditional equations of motion for us for a constant gravitational force. What are the general equations? Now, what constrains this problem? How can you factor those constraints into those equations? Write things out and show us your work.

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