# Help with homework problems please

1. Apr 20, 2006

A cannon is mounted 50m away from the edge of a cliff that drops 10m to the plain below. If the cannon projecticle is fired with an initial velocity of 75 m/sec find the angle of elevation so that the shell lands closest to the cliff face from the plane below.

2. Apr 20, 2006

### Hootenanny

Staff Emeritus
Welcome to PF!

Please show some working and / or intial thoughts. In addition we have a section dedicated to homework or coursework questions.

~H

Note to mentors: please move to Intro Physics

3. Apr 20, 2006

i have no clue i am new to physics this is hard as heck so many formulas but.. ah could someone explain to me how to do this i'm confused

4. Apr 21, 2006

### Hootenanny

Staff Emeritus
Basically, you can split the velocity into two components, one vertical (in the y-direction), and one horizontal (in the x-direction). The projectile is fired at an angle, therefore we need to resolve the velocity vector into it's x and y components. If we let $\theta$ be the angle of elevation above the horizontal the x and y components are;

$$v_{x} = 75\cos\theta$$

$$v_{y} = 75\sin\theta$$

Vertical motion is independant of horizontal motion. Using kinematic equations can you find an expression for the time of flight of the projectile? HINT: Just consider vertical motion.

~H

5. Apr 21, 2006

ah im just to confused which formula do i use?

6. Apr 21, 2006

### nrqed

Itis very very difficult to cover stuff from the ground up on such a forum. We can not replace your teacher or textbook. There is only so much that can be done here. The best way to use the homework section is to learn most of the material in class or in a book in order to learn and understand the fundamentals. Then, if you are stuck on a specific issue or calculation, people can help efficiently.