Escape Velocity Given Radius of 2 Objects

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Discussion Overview

The discussion revolves around calculating the escape velocity from a white dwarf and a neutron star, both having a mass equivalent to one solar mass. Participants explore the implications of unit conversions and the accuracy of classical calculations in extreme gravitational fields.

Discussion Character

  • Technical explanation
  • Homework-related
  • Debate/contested

Main Points Raised

  • One participant presents a calculation for escape velocity using the formula V = sqrt(2GM/R) but receives partial credit, indicating a potential error.
  • Another participant points out that the mass should be converted to kilograms, noting that a solar mass is approximately 2e30 kg.
  • Concerns are raised about the applicability of classical mechanics for calculating escape velocity from a neutron star, as it approaches the speed of light.
  • A participant expresses curiosity about the correct escape velocity values after addressing the conversion issue, suggesting a significant difference in expected results.
  • Another participant emphasizes the importance of reasoning about the results, questioning whether the calculated speeds align with expectations based on physical intuition.
  • Checking units is recommended as a method to avoid errors in calculations.

Areas of Agreement / Disagreement

Participants generally agree on the need for correct unit conversions and the limitations of classical calculations in extreme conditions. However, there is no consensus on the final correct values for escape velocity or the implications of the calculations.

Contextual Notes

The discussion highlights the dependence on proper unit conversions and the challenges of applying classical physics in scenarios involving neutron stars and white dwarfs, where relativistic effects may become significant.

Who May Find This Useful

This discussion may be useful for students and enthusiasts interested in astrophysics, gravitational physics, and those looking to understand the nuances of escape velocity calculations in extreme environments.

bigman8424
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Got a dosie of a problem I need checked. I've been playing around with this problem, and after I submit the right answer (the ans. I got) , it came out wrong. Someone tell me what I'm doing wrong PLEASE thanks:

The prob. is to calculate escape velocity from a white dwarf and a neutron star. They are each 1 solar mass. The white dwarf has a radius of 104 km + the neutron star has a radius of 10 km.

Step I took:
sqr. root of 2GM/R = V = Sqroot of (2)(6.67e(-11)(1) all over 10^4th power
v = 1.15e(-7)

neutron star v= (2)(6.67e(-11)(1) all over 10
v = 3.65e(-6)
i got that, but only got half credit for this prob., what did I do wrong or have to add??
thanks
 
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Looks like you forgot to convert the mass of the objects to kg. You put in "1" for both cases, but a solar mass is equal to 2e30 kg.

Also note that the escape velocity from a neutron star is near the speed of light, so the classical calculation you did won't be very accurate.
 
Last edited:
Converting to Kg

Oh I see so I did the prob. right, but just messed up on the conversions, so close. Just out of curiosity what the correct answer would be, is it going to be V = 1.15 e-10 and for the neutron star 3.65e-9

just trying to learn this, so i don't mess up next time

thanks a lot
 
Whenever you get an answer, you should always go back and think if it makes sense. Would you expect it to take more or less speed to escape from a neutron star than, say, the earth? Does that check with the equation you used? Next, look at your answer. How fast is 10-10 m/s? Is it faster or slower than you can run? If you start running around, do you escape the Earth's gravity?
 
you should also check your units! this will always helps.
 
Last edited:

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