# Horizontal Recoil Speed of gun

## Homework Statement

a 1200kg gun mounted on wheels shoots an 8kg projectile with a muzzle velocity of 600m/s at an angle of 30degrees above the horizontal. find the horizontal recoil speed of the gun

## Homework Equations

KE= .5mvfE2 - .5MViE2

## The Attempt at a Solution

rock.freak667
Homework Helper
What is happening is that the projectile is being shot out of the gun, so the impact of the projectile leaving is causing the recoil.

What principle do you know involves collisions and impacts?

elasticity?

or perhaps momentum?

rock.freak667
Homework Helper
or perhaps momentum?

Right and in any sort of collision momentum is conserved. However, you have the gun at an angle, so you need to apply the conservation law in both horizontal and vertical directions.

can you please explain the conservation law to me - I have read the book several times but our language is not attuned.

In a simple way please tell me what it means. thanks

I have tried everything I can think of with momentum but I don't understand about the law of conservation of momentum and impulse - I think this is my problem.

rock.freak667
Homework Helper
can you please explain the conservation law to me - I have read the book several times but our language is not attuned.

In a simple way please tell me what it means. thanks

I have tried everything I can think of with momentum but I don't understand about the law of conservation of momentum and impulse - I think this is my problem.

Essentially it is that the total momentum in a closed system is zero.

or in easier terms

the momentum before the event = momentum after the event
(in a given direction).

Remember that momentum is only conserved when no external force acts on the system.
momentum along X is anyway conserved
But for Y, if you take gun and bullet as system then its not conserved
its conserved only when you system is GUN+BULLET+EARTH

well you'll say that it doesn't matter what i consider as system as momentum is conserved anyway but in more complex problems especially when friction is involved, not considering right system makes problems difficult and maybe also lead to wrong answer!!!