Solving for Impact Velocity: A Bullet of Ice at 0°C

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Homework Help Overview

The problem involves calculating the impact velocity of a bullet of ice at 0°C, specifically to determine the velocity required to melt 68% of the ice upon impact. The context includes the conversion of kinetic energy into thermal energy for melting the ice.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the relationship between kinetic energy and the energy required to melt the ice, questioning the use of the 68% figure in calculations. There are attempts to equate kinetic energy with the energy needed to melt a portion of the mass of ice.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of the problem. Some have provided insights into the equations involved, while others express confusion and seek further clarification on the steps to arrive at the solution.

Contextual Notes

There is a focus on the assumption that all kinetic energy is converted into melting ice, and participants are grappling with how to appropriately apply the percentage of ice that melts in their calculations.

noobatphysics
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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
 
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Why didn't you use the 68%? The kinetic energy turns into the energy needed to melt 0.68m, not m.
 
um I am still puzzled
LOL
can u show me the steps?
 
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.
 
oh i see...

i got... 674 m/sec

doesn't seem right

Ek = 334800 x .68?
 

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