Velocity of an apple before strikes the surface of a white dwarf.

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Homework Help Overview

The problem involves calculating the velocity of an apple dropped from a significant height above the surface of a white dwarf, with specific values given for the height, mass, and gravitational acceleration of the white dwarf.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the application of gravitational equations and question the assumptions regarding constant acceleration. There are attempts to relate the mass and radius of the white dwarf to the gravitational acceleration experienced by the apple.

Discussion Status

Some participants have suggested the need to find gravitational acceleration as a function of distance and consider potential energy, while others express uncertainty about the necessity of using integrals. There is an ongoing exploration of different approaches to the problem without a clear consensus on the best method.

Contextual Notes

Participants note the significant height from which the apple is dropped and question the relevance of using constant acceleration equations in this context. There is also mention of the radius of the white dwarf and its comparison to Earth's radius, indicating potential misunderstandings about the scale involved.

ScienceGeek24
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Homework Statement



An apple is dropped from a height of 12.8*10^6 m above the surface of the white dwarf. With what speed does the apple strike the surface of the white dwarf?

M of white dwarf= 1.99*10^30
gravity of white dwarf= 3.29*10^6

Homework Equations



Vf^2=Vi^2+2a(deltaX)

The Attempt at a Solution



I tried doing this v=srqt( 2(3.29*10^6)(12.8*10^6 ) and my result was far of the real answer i got 9.17*10^6 m/s and the answer sheet showed 5.28 *10^6 m/s.

What did I do wrong?
 
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Hi ScienceGeek24 :smile:

(try using the X2 button just above the Reply box :wink:)
ScienceGeek24 said:
I tried doing this v=srqt( 2(3.29*10^6)(12.8*10^6)

that's only for constant acceleration

a white dwarf is only about the size of the Earth, so 107 m is a long way up

you'll need the radius …

isn't there a relation between the radius and mass of a white dwarf? :smile:
 
yes a=Gm/r^2 that's how i got the acceleration of the white dwarf

The radius is equal of the Earth's radius which is 6.37*10^2 and the mass was the same the sun which was 1.99*10^30. However, I still don't understand your question.

 
You'll need to find the gravitational acceleration as a function of distance, and integrate (or use potential energy). :wink:
 
tiny-tim said:
Hi ScienceGeek24 :smile:

(try using the X2 button just above the Reply box :wink:)



ScienceGeek24 said:
yes a=Gm/r^2 that's how i got the acceleration of the white dwarf

The radius is equal of the Earth's radius which is 6.37*10^2 and the mass was the same the sun which was 1.99*10^30. However, I still don't understand your question.

tim's suggestion referred to super-scripts, not the whole post, so your post would look like:
ScienceGeek24 said:
yes a=Gm/r2 that's how i got the acceleration of the white dwarf

The radius is equal of the Earth's radius which is 6.37*102 and the mass was the same the sun which was 1.99*1030. However, I still don't understand your question.
BTW: Earth's radius is significantly greater than 6.37*102m !
 
The thing is that i don't think this problem should be base with integrals, it has to be an easier way, sqrt(3.27*106)(12.8*106+6.37*106) and still i don't get the right answer.

I mean there has to be another factor that I am not taking into account. I know this problem does not need integrals.
 

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