Answer:
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
