Projectile fired to melt ice

  • Thread starter Walley1
  • Start date
  • #1
10
0

Homework Statement


Newt needs to melt some ice, so he fires a test projectile (0.025 kg) at 30.0 degrees C at a speed of 240 m/s into a large block of ice at 0 degrees C, in which it becomes embedded (comes to rest). Approximately what mass of ice melts? (i.e. ignore the heat lost by the projectile in going from 30-0 degrees C).


Homework Equations


e=(mv^2)/2


The Attempt at a Solution


The heat of fusion of water is 3.35x10^5J.
e=(0.025 * 240^2)/2=720J
720J/3.35x10^5J=0.002, so 0.002kg of ice melts.
I get the feeling that's incorrect, especially since I didn't do anything with the temperature (although it mentions that I should ignore the heat lost by the projectile).

Thanks for any help you can provide.
 

Answers and Replies

  • #2
1,198
5
Energy release of the projectile is its kinetic energy. So assuming the ice is at 0 C, the amount that melts equals the projectile KE divided by the latent heat of the ice. The rotational kinetic energy of the projectile is omitted. This is what you have done and it is correct. I assume the heat of fusion of ice is 3.35X10^5 J/kg. You left off the kg.
 
  • #3
10
0
Energy release of the projectile is its kinetic energy. So assuming the ice is at 0 C, the amount that melts equals the projectile KE divided by the latent heat of the ice. The rotational kinetic energy of the projectile is omitted. This is what you have done and it is correct. I assume the heat of fusion of ice is 3.35X10^5 J/kg. You left off the kg.

Thanks a million!
 

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