Answer:
 v = 16.11 m / s
Step-by-step explanation:
For this exercise we must use the principle of conservation of energy. We set a reference system on the part of the platform without elongation 
starting point. When the spring is compressed 
 Em₀ = K_e + U = ½ k x² + m g x ’ 
final point. The point where it leaves the platform 
 Em_f = K = ½ m v² 
energy is conserved 
 Em₀ = Em_f 
 ½ k x² + m g x ’= ½ m v² 
 v² = 
 x² + g x
 x² + g x 
let's calculate 
 v² = 
 1.25² + 9.8 1.25
 1.25² + 9.8 1.25 
 v² = 247.159 + 12.25 = 259.409 
 v = 16.11 m / s