Question about supernova kinetic energy

AI Thread Summary
The discussion focuses on calculating the kinetic energy of a supernova explosion and the volume of interstellar gas swept up by the ejecta. The kinetic energy is derived using the virial theorem, although it's noted that this theorem is more applicable on larger scales rather than near a supernova. The user is confused about determining the swept volume as the outflow velocity decreases. The importance of using kinematical models for accurate calculations in this context is emphasized. Understanding these principles is crucial for solving the problem effectively.
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A9: Supernova Remnants
Consider a supernova explosion in the outer 4M⊙ of a dying star, ejected at a speed of 5000 km/s.
a ◮ What is the kinetic energy of the expanding ejecta?
b ◮ The ejecta are slowed by sweeping up the local interstellar gas. Assuming the density of the interstellar gas
is ig = 2 × 10−19 kg/m3, how large a volume will be swept up by the time the outflow velocity has decreased
to 10 km/s? HINT: Assume the KE of the expansion is conserved.
A10:
 
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Part a I used virial theorem for kinetic energy 3mv^2 and for part b I used mass= density / volume but am confused with swept volume
 
Virial theorem is only useful on large scales, for a region near a supernova event you still need to use kinematical models.
 

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