57 = 95*sqrt(1-v^2/(3*10^5)^2)
57/95 = sqrt(1-v^2/(3*10^5)^2)
Возведем обе части в квадрат
3249/9025 = 1-v^2/(3*10^5)^2
3249/9025 -1 = -v^2/(3*10^5)^2
-5776/9025 = -v^2/(3*10^5)^2
5776/9025 = v^2/(3*10^5)^2
v^2 = 5776*(3*10^5)^2/9025
v = sqrt(5776*(3*10^5)^2/9025)
v = 76*3*10^5/95 = 2.4*10^5 = 2.4*100000 = 240000
Ответ: 240000