Xittenn Posted April 1, 2012 Posted April 1, 2012 1) A lion of mass 120 kg leaps at a hunter with a horizontal velocity of 12m/s. The hunter has an automatic rifle firing bullets of mass 15 g with a muzzle speed of 630m/s and he attempts to stop the lion in midair. How many bullets would the hunter have to fire into the lion to stop its horizontal motion? Assume the bullets stick inside the lion. I'm not sure if this was a textbook question or a question my professor conjured up, but I had to laugh!
Joatmon Posted April 1, 2012 Posted April 1, 2012 (edited) 1) A lion of mass 120 kg leaps at a hunter with a horizontal velocity of 12m/s. The hunter has an automatic rifle firing bullets of mass 15 g with a muzzle speed of 630m/s and he attempts to stop the lion in midair. How many bullets would the hunter have to fire into the lion to stop its horizontal motion? Assume the bullets stick inside the lion. I'm not sure if this was a textbook question or a question my professor conjured up, but I had to laugh! Just a few details to complicate the issue. When the bullets leave the rifle they are still accelerating and as they travel they stop accelerating and start slowing. How rapidly can the rifle be fired and so can enough bullets be pumped into the lion in the time available? I think a bullet that hits only soft tissue and travels well into the lion will have less of a slowing effect than one hitting bone and travelling less distance into the lion ( not too sure about that). How much effect has air resistance on the lion's velocity while this is going on? I would strongly advise you to not to mention these small details - your professor may think you are taking the p**s! See:- http://thefiringline...hp?t-21814.html Edited April 1, 2012 by Joatmon
ewmon Posted April 1, 2012 Posted April 1, 2012 (edited) Of all the things I know about physics, I get confused in problems like this between energy and momentum, but I think we need to look at energy here. So Xittenn, in terms of grams∙meters/second, can you compute the kinetic energy of the lion and of a bullet, and then take the next step to determine how many bullets would have the KE of the lion, thus canceling out its motion? As for the gun, let's assume that the hunter is using this nasty beast of a weapon by Metal Storm, a multiple-barrel weapon that works like a roman candle and fires more than 1,000,000 rounds per minute. Edited April 1, 2012 by ewmon
Joatmon Posted April 1, 2012 Posted April 1, 2012 (edited) Of all the things I know about physics, I get confused in problems like this between energy and momentum, but I think we need to look at energy here. So Xittenn, in terms of grams∙meters/second, can you compute the kinetic energy of the lion and of a bullet, and then take the next step to determine how many bullets would have the KE of the lion, thus canceling out its motion? As for the gun, let's assume that the hunter is using this nasty beast of a weapon by Metal Storm, a multiple-barrel weapon that works like a roman candle and fires more than 1,000,000 rounds per minute. Ouch - that might just do it - lol! Only 180 bullets from such short barrels might not be enough? Edited April 1, 2012 by Joatmon
Xittenn Posted April 1, 2012 Author Posted April 1, 2012 The answer is 153 . . . . but the point was, it is a punny question. Momentum is conserved, energy form is not conserved in an inelastic collision! And to be clear, if the bullet continues to accelerate post muzzle it is because of a pressure gradient that still exists exterior to the channel. A force must be present for acceleration to occur.
Joatmon Posted April 1, 2012 Posted April 1, 2012 (edited) The answer is 153 . . . . but the point was, it is a punny question. Momentum is conserved, energy form is not conserved in an inelastic collision! And to be clear, if the bullet continues to accelerate post muzzle it is because of a pressure gradient that still exists exterior to the channel. A force must be present for acceleration to occur. There is a force for a short distance because as the bullet leaves the barrel the ejected expanding gasses behind it continue to exert force although this force is soon dissipated. Under unrealistic conditions, say a barrel something like 20m long there may not be enough expanding gas to keep the bullet accelerating the full length of the barrel and then push a little more on exit. "3-2. Transitional Ballistics Sometimes referred to as intermediate ballistics, this is the study of the transition from interior to exterior ballistics. Transitional ballistics is a complex science that involves a number of variables that are not fully understood; therefore, it is not an exact science. What is understood is that when the projectile leaves the muzzle, it receives a slight increase in MV from the escaping gases. Immediately after that, its MV begins to decrease because of drag. " Just giving my (British) sense of humour an outing! Edited April 1, 2012 by Joatmon
Xittenn Posted April 1, 2012 Author Posted April 1, 2012 (edited) What, British humour? Edited April 1, 2012 by Xittenn
Joatmon Posted April 1, 2012 Posted April 1, 2012 (edited) What, British humour? No, the fact that nobody else is able to appreciate it. (Two nations divided by a common language?) Edited April 1, 2012 by Joatmon
Xittenn Posted April 1, 2012 Author Posted April 1, 2012 My brother watches Coronation St. everyday, which is so odd for a young man his age who is divided by a common language. I'm into like action, sci-fi, horror, and thriller so honestly I haven't the foggiest, but he seems to like it . . . . it's his favorite show. He makes his buddies watch it when they come over to chum. :/
Joatmon Posted April 1, 2012 Posted April 1, 2012 (edited) My brother watches Coronation St. everyday, which is so odd for a young man his age who is divided by a common language. I'm into like action, sci-fi, horror, and thriller so honestly I haven't the foggiest, but he seems to like it . . . . it's his favorite show. He makes his buddies watch it when they come over to chum. :/ I hope your brother and his friends realise it's not a comedy. (or at any rate it's not supposed to be) Edited April 1, 2012 by Joatmon
Xittenn Posted April 1, 2012 Author Posted April 1, 2012 Isn't it? Oh well . . . . . . got anymore funny homework problems???
Cap'n Refsmmat Posted April 1, 2012 Posted April 1, 2012 My thermodynamics homework asked me to approximate the entropy of a moose. 1
mississippichem Posted April 1, 2012 Posted April 1, 2012 (edited) My thermodynamics homework asked me to approximate the entropy of a moose. All I know is that a collision with a moose is not an elastic one, and as a process is not in general reversible. Though dS>0 for the system just the same. Edited April 1, 2012 by mississippichem 1
Xittenn Posted April 1, 2012 Author Posted April 1, 2012 How much entropy in the form of moose would one have to throw at a car to stop it?
Joatmon Posted April 1, 2012 Posted April 1, 2012 (edited) How much entropy in the form of moose would one have to throw at a car to stop it? Please be aware that if you want to test this by practical experiment the law on roadkill is quite complicated. You may break the law if you take the moose home as food. The next car that finds the dead moose may not be breaking the law if it takes the moose home.The following is from the link:- http://en.wikipedia....ear:_US_Special "The next car that comes along and finds a dead moose may not be breaking the law if they take it home for food.As Hammond and May set up camp, Clarkson went to look for more roadkill; he came back with an enormous dead cow, placed on the roof of the Camaro, which May refused to eat." Edited April 1, 2012 by Joatmon 1
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now