Flying blind here.....but here's my best attempt
Here's the equation we need....
KE = (1/2) m * v^2 fill in what we know
50000 = (1/2)(1000 kg) * v^2
1 joule = 1kg * m^2/^2 ....so we have
50000 kg (m^2 /s^2) = (1/2) (1000 kg) * v^2 cancel the kg and simplify
50000 (m^2/ s^2) = 500 v^2 divide both sides by 500
100 (m^2 /s^2) = v^2 take the square root of both sides
10 m /s = velocity