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

AI Thread Summary
To determine the impact velocity needed to melt 68% of a bullet of ice at 0°C, the kinetic energy equation (1/2mv^2) must be equated to the energy required to melt the specific mass of ice (Q = ml). The correct approach involves recognizing that only 68% of the mass is melted, so the equation should reflect this by using 0.68m in the energy calculation. The resulting equation leads to the conclusion that the impact velocity is approximately 674 m/sec. Clarification on using the correct mass percentage is essential for accurate 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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