Answer:
<em>0.85c </em>
Explanation:
Rest mass of Kaon 
= 494 MeV/c²
Rest mass of proton 
= 938 MeV/c²
The rest energy is gotten by multiplying the rest mass by the square of the speed of light c²
for the kaon, rest energy 
= 494c² MeV
for the proton, rest energy 
= 938c² MeV
Recall that the rest energy, and the total energy are related by..
= γ
which can be written in this case as
= γ ...... equ 1
where = total energy of the kaon, and
= rest energy of the kaon
γ = relativistic factor = 
where 
But, it is stated that the total energy of the kaon is equal to the rest mass of the proton or its equivalent rest energy, therefore...
= ......equ 2
where is the total energy of the kaon, and
is the rest energy of the proton.
From = = 938c²
equ 1 becomes
938c² = γ494c²
γ = 938c²/494c² = 1.89
γ = = 1.89
1.89
= 1
squaring both sides, we get
3.57( 1 - 
) = 1
3.57 - 3.57 = 1
2.57 = 3.57
= 2.57/3.57 = 0.72
= 0.85
but,
v/c = 0.85
v = <em>0.85c </em>
