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Latent Hear

  • #1

Homework Statement


A Bullet of ice at a temperature of 0 degrees celieus is fired into a target
Assuming that all the impact energy is retained by the ice
what impact velocity is needed to melt 68% of the ice

Homework Equations



1/2mv^2
Q = ml

The Attempt at a Solution


i got..
v^2 = 668000
i doubt that is the correct answer
can some show me the steps to work this out
 

Answers and Replies

  • #2
ideasrule
Homework Helper
2,266
0
Why didn't you use the 68%? The kinetic energy turns into the energy needed to melt 0.68m, not m.
 
  • #3
um im still puzzled
LOL
can u show me the steps?
 
  • #4
ideasrule
Homework Helper
2,266
0
I thought you used:

1/2mv^2
Q = ml

and equated them to get:

1/2mv^2=ml
v^2=2l

The statement 1/2mv^2=ml means "all the kinetic energy turns into the energy needed to melt the mass". However, only 68% of the mass melts, so the kinetic energy has to equal 0.68ml.
 
  • #5
oh i see....

i got... 674 m/sec

doesn't seem right

Ek = 334800 x .68?
 

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