PARISâ€”Masked gunmen stormed the offices of French satirical magazine Charlie Hebdo on Wednesday, killing a dozen people and decimating a newsroom that long took pride in defying the outrageâ€”and death threatsâ€”stirred by its caricatures lampooning Islam. The brutal rampage shocked a nation that has been living in dread of reprisal attacks since joining the fight against Islamist insurgents in Africa and the Middle East. The attackâ€”by gunmen armed with AK-47 riflesâ€”triggered an outpouring of public anger at home and expressions of solidarity from around the world. I think you have all heard of this dramatic event that happened this week. All around the world People are shocked and in a lot of drawings were posted in response. This one below is in my opinion one of the strongest statements. It shows a wall were the French National Motto LibertÃ©, Ã‰galitÃ©, FraternitÃ©, French for "Liberty, equality, fraternity", is written on a wall and the word Liberty is shot through with bullets as a symbol of the attack against the freedom of press.
Thatâ€™s where the physics now comes in:
If there are 17 bullet-holes in the wall and the gun shoots each 10gram Bullet with 250m/s in a total time of 4sec. Determine the Frequency of the gun, the Kinetic Energy of a bullet right before it hits the wall and the approximate distance the shooter stood away from the wall. (Neglect air-residence)
Letâ€™s start with the Kinetic Energy of the bullet. To solve this Question you can use the formula (1/2)mv2 which if you substitute with units equals 312.5 Joules
Frequency is the number of revolutions that occur in a second; so in this case we would have 4.25 Hz
To find out the distance the shooter stood away from the wall you should know, once the bulled is fired there will be no horizontal acceleration which will help us in the formula to finde the distance. But first we have to solve for the time it takes one bullet to get from the gun to the wall. As we know that 17 bullets were fired in 4seconds we simply have to divide the time it took all of them by the number of Bullets and then we get .24sec. for each Bullet.
Now that we know that we can substitute in the formula d=vit+(1/2)at2 and as I already mentioned a=0 which makes the equation even shorter so it really only is d=vit which gives us a distance of 59m.
For anyone who is more interested in the whole story there is a link to the Guardian where there is a live report about the event.