# I'm stuck on cannon ball qusetion can any one help

1. Sep 26, 2006

### jgerco

the question is how far away was a cannonball fired?

we know that the
-cannonball ricocheted along the ground an unknown amount of times before hitting the persons kneecap and shattering it.
-a three pound cannon ball has a mass of 1.36kg
-the maximum range of the cannon is 1125m
-the maximum elevation of the cannon is 30 degrees
-the cannon was on flat ground
-acceleration due to gravity is 9.8 ms-2
-no air resistance
-a kneecap is 1 cm thick
-the force needed to break a kneecap is 12000 N
-the cannon ball was about to hit the ground
-the cannon muzzle was at the same height as his knee
-the angle of incidence and reflection are the same 30 degrees for evry time it hits the ground
-each time the ball hits the ground its kinetic energy is reduced by 75%

any help to this question would be much appreciated and if you think you have the answers to my question could you please e-mail me at mmm_freak@yahoo.com.au thank you

2. Sep 27, 2006

### Andrew Mason

Kind of an odd question. But it provides some little clues.

Use the information about the cannon ball trajectory to determine the muzzle velocity of the cannon ball. Since the ball hits the ground with an angle of incidence of 30 deg. what does that tell you about the firing angle?

The problem with this question is that the cannon ball can break the knee on any number of bounces, so I don't see that there would be just one answer.

AM