nemofi Posted August 4, 2008 Share Posted August 4, 2008 Please help me solve this equation? (a to the power 9)-(b to the power 9) what is the reaction force experienced by a soldier shooting with a rifle? Plz help me Martin with explanation. Link to comment Share on other sites More sharing options...
Klaynos Posted August 4, 2008 Share Posted August 4, 2008 I don't think you've got enough information [math]a^9 - b^9[/math] Cannot be solved unless it's = something, and even then you'd need another equation because you've got two unknowns. To answer you second question, what are newtons 3 laws? Link to comment Share on other sites More sharing options...
John Cuthber Posted August 4, 2008 Share Posted August 4, 2008 I'd quite like to know where you get the ninth power of anything in a physical system. Link to comment Share on other sites More sharing options...
Martin Posted August 5, 2008 Share Posted August 5, 2008 what is the reaction force experienced by a soldier shooting with a rifle? ... You need some numbers. Maybe the bullet mass is 20 grams (0.02 kg) and the speed of the bullet is 300 meter per second so the momentum of the bullet is 6 units, in the usual SI system of units. That means that the rifle gets a kick back of 6 units. this is dissipated against the man's shoulder in a certain period of time which you can estimate. What is the mass of the rifle? Say it is 6 kilogram. Then if the rifle is free to move it will have a backward speed of 1 meter per second. I estimate that the man's body can absorb the kick of the rifle in 0.1 second. So the force in Newtons will be 6/.1 = 60 Newtons. The force on the man depends a lot on how long he has to absorb it! If the impulse is spread out over a fairly long period of time like 0.1 second then you see the force is mild, like here 60 Newtons is not so much (like 6 kilogram force) This depends on how much give his shoulder has. The good thing about having a massive rifle is that it moves back slowly (for a given amount of kick) and will be easier for the man to absorb the impulse while keeping his stance. So you must put in some numbers. I think. My numbers are just rough guesswork. To really answer you must get the real numbers. The mass of the bullet, the muzzlevelocity, the mass of the rifle etc. How many centimeters of "give" you want in the man's shoulder. OK? then you can really tell what force the soldier will experience. Link to comment Share on other sites More sharing options...
insane_alien Posted August 5, 2008 Share Posted August 5, 2008 well, modern rifles(particularly those used in combat eg. by a soldier) tend to be made as light as possible so they are easy to carry. they do indeed deliver a larger kick than older heavier rifles. but either of them, if held wrong can shatter your collar bone or dislocate your shoulder with ease if held in the wrong position. Link to comment Share on other sites More sharing options...
Martin Posted August 5, 2008 Share Posted August 5, 2008 well, modern rifles(particularly those used in combat eg. by a soldier) tend to be made as light as possible so they are easy to carry.... I thought they might be. Thanks. How about giving us some more realistic numbers? Just thinking about single-shot mode (not automatic fire) what would be a good example for a student to work? What mass rifle? What mass bullet? What muzzle velocity? Since this guy is new, and he asked, it might be nice to have some definite specs. Link to comment Share on other sites More sharing options...
insane_alien Posted August 5, 2008 Share Posted August 5, 2008 well, for the rifle i've fired most (SA-80) the specs are Rifle Mass: 3.8kg Bullet Mass: 0.004kg Muzzle Velocity: 940m/s single fire would be the best way to do it as multiple shots change the way your body absorbs the shock(it is impossible to keep on target for more than say 3 shots). Link to comment Share on other sites More sharing options...
foodchain Posted August 5, 2008 Share Posted August 5, 2008 well, modern rifles(particularly those used in combat eg. by a soldier) tend to be made as light as possible so they are easy to carry. they do indeed deliver a larger kick than older heavier rifles. but either of them, if held wrong can shatter your collar bone or dislocate your shoulder with ease if held in the wrong position. I don’t know if it will break your bones, don’t know all the angles though. I know if you take a modern rifle and press your nose up to it such is rather painful, nothing broke though:D. Then again as pointed out a lot of this is rifle dependent. Link to comment Share on other sites More sharing options...
insane_alien Posted August 5, 2008 Share Posted August 5, 2008 it can definitely break you bones, i've seen it happen and it isn't pretty. although if you hold it correctly the worst you have to fear is a 'dead' arm after firing off a lot of shots. Link to comment Share on other sites More sharing options...
Klaynos Posted August 5, 2008 Share Posted August 5, 2008 it can definitely break you bones, i've seen it happen and it isn't pretty. although if you hold it correctly the worst you have to fear is a 'dead' arm after firing off a lot of shots. Seconded, Link to comment Share on other sites More sharing options...
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