is it true that if you dropped a penny from a height (eiffle tower) you would kill someone and how does it work?

Question: is it true that if you dropped a penny from a height (eiffle tower) you would kill someone and how does it work?
- Keywords:
  drop,
  eiffel tower,
  height,
  penny
Asked by idunno to Cesar, Emily, Jamie, Kate, Philippa on 18 Jun 2011.
- Jamie Gallagher answered on 16 Jun 2011:
  
  Hi,
  Well lets have a little think about it. Physics fun.
  
  a penny weighs 1.46g and the eiffle tower is 324m tall- so we can work out the poternial energy.
  Ep=mgh (mass x gravityx height)
  Ep=0.00146 x 9.8 x324
  Ep=4.6 J
  
  convert this to kinetic energy
  Ek=1/2 mv^2 (mass x velocity squared)
  v=sqrt(2E/m)
  v=79.2 m/s
  
  So by the time it gets to the ground it will be traveling at almost 80 meters every second! That will make quite a thud then it hits you.
  
  The reason that it goes so fast is due to gravity. This force acts on us all and it is an acceleration, it constantly increases the speed of a falling object.
  
  I do not know if this would kill someone. Why don’t you try dropping a penny from the height of your head and listen to how hard it hits the ground. You can see that it would be dangerous if it was going many times faster.
  
  Just remeber I have noted this down quickly and I have also made assumptions such as concervation of energy and no air resistance.
- Cesar Lopez-Monsalvo answered on 17 Jun 2011:
  
  Hey
  
  This actually was a little bit of fun. Although I agree with Jamie’s maths, the fact that he is not taking into account the air resistance and the shape of the penny is quite crucial.
  
  Say first that we ignore the air resistance, even the 79.2 m/s…some 180 mph, is not fast enough to penetrate your skin! You can compare that with a small bullet of about the same mass of a penny shot by a gun. The bullet obviously penetrates your skin, but it also travels at around 600 mph…much faster than the final velocity of the coin. Also, the surface that gets in contact with your skin is much smaller for the bullet, so it is very unlikely that the coin will actually break your skin, even if it hits you on its side.
  
  But this was the worst case scenario, in reality, taking into account the air resistance is very hard because a penny is affected very severely by the wind. Some estimates indicate that the terminal velocity of the penny would be no greater than 50 mph…really very low. It would probably be painful, but no serious harm will be made.
- Kate Clancy answered on 17 Jun 2011:
  
  That was fun, reading your two answers. Even buffeted by wind, I don’t think I’ll take my chances. So idunno, if you ever feel like throwing a penny off the Eiffel Tower, please warn me first! 🙂
- Emily Robinson answered on 17 Jun 2011:
  
  Thats why they have nets under the eiffle tower to catch the coins!
- Philippa Demonte answered on 18 Jun 2011:
  
  @idunno I think that even if the falling velocity (speed) of the penny weren’t enough to kill someone, the shock of it would! *goes to put hard hat on*