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
Messages
6
Reaction score
0

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
 
Physics news on Phys.org
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?
 
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
View full post »

Thread 'Struggling to understand the concept of this question (ice cube in water optics question)'

TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...
View full post »

Similar threads

Thermodynamics, bullet melting ice problem
Replies
4
Views
2K
Ice melted by impact of lead bullet
Replies
10
Views
3K
I try to solve a thermodynamics problem on heat transfer
Replies
3
Views
2K
How Does a Bullet Impact Affect the Angular Velocity of a Door?
Replies
3
Views
3K
What is the Velocity of the Ball After Impact?
Replies
7
Views
2K
Heat transfer, how long it takes ice to reach melting point
Replies
6
Views
4K
Solving Heat Transfer Problem with Melting Ice Cube
Replies
4
Views
4K
Velocity of bullet before hitting a pendulum
Replies
11
Views
3K
Thermodynamics Ice Melting Question
Replies
4
Views
3K
Mass of Ice required to achieve a certain final Temperature
Replies
3
Views
2K

Hot Threads

Recent Insights

Back
Top