Answer:
The value is [tex]v_y = -48.61 \ m/s[/tex]
Explanation:
From the question we are told that
  The horizontal speed is  [tex]u_x = 252 \ m/s[/tex]
  The horizontal distance is  [tex]d = 1250 \ m[/tex]
Generally the time taken by the hot magma in air before landing is mathematically represented as
    [tex]t = \frac{d}{u_x}[/tex]
=> Â Â [tex]t = \frac{ 1250 }{252}[/tex]
=> Â Â [tex]t = 4.96 \ s[/tex]
Generally the initial vertical velocity of the magma when it was lunched is Â
  [tex]u_y = 0 \ m/ s[/tex]
Then the final velocity of the magma when it hits the ground is mathematically represented s
    [tex]- v_y = u_y + gt[/tex]
Here the negative sign mean that the direction of the velocity is towards the negative y -axis
So Â
    [tex]- v_y = 48.61 \ m/s[/tex]
=> Â Â [tex]v_y = -48.61 \ m/s[/tex]
