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Time dilation calculation

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    Q) the lifetime of a star is 10billion years as measured by an observer at rest with respect to the star. The star is moving away from the Earth at a speed of 0.81c.
    Calculate the lifetime of the star according to an observer.

    A) 17.1 billion

    But plugging the numbers in to find t' I get 16.6billion. What's correct?
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    (Original post by Feynboy)
    Q) the lifetime of a star is 10billion years as measured by an observer at rest with respect to the star. The star is moving away from the Earth at a speed of 0.81c.
    Calculate the lifetime of the star according to an observer.

    A) 17.1 billion

    But plugging the numbers in to find t' I get 16.6billion. What's correct?
     t'=\frac{1}{\sqrt{1-v^2/c^2}}t=\frac{1}{\sqrt{1-0.81^2}}10=17.05 billion years
 
 
 
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