# 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