Given a change in internal energy, how can I find the temperature

In summary, two lead bullets with different masses and velocities collide head-on and stick together, resulting in a change in kinetic energy of the system that appears entirely as increased internal energy. The bullets are both originally at a temperature of 30.0°C, and we need to determine the temperature and phase of the combined bullets after the collision. Using the specific heat, melting point, and latent heat of fusion for lead, we can calculate the heat required to raise the temperature of the bullets to the melting point. This is found to be 860J out of the total change in internal energy of 1098J. The remaining energy goes into melting the bullets, but further calculations are needed to determine the final temperature and phase of the combined bullets
  • #1
mp0295
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Homework Statement


Two speeding lead bullets, one of mass 15.0 g moving to the right at 270 m/s and one of mass 7.65 g moving to the left at 390 m/s, collide head-on, and all the material sticks together. Both bullets are originally at temperature 30.0°C. Assume the change in kinetic energy of the system appears entirely as increased internal energy. We would like to determine the temperature and phase of the bullets after the collision. (Lead has a specific heat of 128 J/(kg K), a melting point of 327.3°C, and a latent heat of fusion of 2.45 104 J/kg.)

(e) What is the temperature of the combined bullets after the collision?

(f) What is the phase of the combined bullets after the collision?
mbullet,solid= ____ g
mbullet,liquid= ____ g


Homework Equations



I have already correctly found the change in internal energy to be 1098J.


Q=mc[itex]\Delta[/itex]T
Q=L[itex]\Delta[/itex]m

The Attempt at a Solution



I really don't know how to do this.

I tried finding the heat required to raise the temperature from 30C to the melting point using Q=mc[itex]\Delta[/itex]T => Q=.0226kg*128J/(kgK)*297.3K and found this to be 860J but I don't know where to go from there.
 
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  • #2
Imagine this was ice instead - you start with ice at -30degC and you heat it ... the ice warms up to 0degC right? Then what?

Same with the bullets - so 860J out of the 1098J goes to warming the bullets until they are ready to melt.
How much energy goes into melting the bullets?
 

1. How is internal energy related to temperature?

The internal energy of a system is the sum of all its microscopic energies, including the kinetic and potential energies of its particles. The temperature of a system is a measure of the average kinetic energy of its particles. Therefore, a change in internal energy can result in a change in temperature.

2. Can I use the ideal gas law to find the temperature?

Yes, the ideal gas law (PV = nRT) can be used to find the temperature if the pressure, volume, and number of moles of gas are known. This equation relates the temperature to the other variables and assumes that the gas behaves ideally.

3. Is there a direct formula to calculate temperature from internal energy?

No, there is not a direct formula to calculate temperature from internal energy. The relationship between the two depends on the specific system and its properties. However, the ideal gas law and other thermodynamic equations can be used to determine the temperature indirectly.

4. How does the specific heat capacity affect the temperature change for a given internal energy change?

The specific heat capacity is a measure of how much energy is required to raise the temperature of a substance by 1 degree Celsius. The higher the specific heat capacity, the more energy is needed to raise the temperature. Therefore, for a given change in internal energy, a substance with a lower specific heat capacity will experience a greater change in temperature compared to a substance with a higher specific heat capacity.

5. Can the temperature change be negative if there is a decrease in internal energy?

Yes, the temperature change can be negative if there is a decrease in internal energy. This is because temperature is a measure of the average kinetic energy of the particles in a system. If the internal energy decreases, it means that the particles are losing energy and their average kinetic energy decreases, resulting in a decrease in temperature.

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