At what speed does a clock move if it is measured to run at a rate two-fifths the rate of a clock at rest with respect to an observer

0.44c

Explanation:

We know that

Time interval at speed (ts)= time interval at rest(tr) / gamma

where

gamma = √[1-(v/c)²]

ts = tr / gamma

tr/ts = gamma

But

Ss/Sr = gamma

Where

Sr = clock speed at rest, Ss at speed):

So

√[1-(v/c)²] = 2/5

1 - (v/c)² = 4/25

(v/c)²= 5/25

v/c = √5 / 5

v = 0.444c

increase masses, decrease separation

the inner core.

good luck: )

klicker