Answer:
The value is
![v_y = -48.61 \ m/s](https://img.qammunity.org/2021/formulas/physics/high-school/oi4mc6oqumk5ofsq6em706plb7kyaol9pw.png)
Step-by-step explanation:
From the question we are told that
The horizontal speed is
![u_x = 252 \ m/s](https://img.qammunity.org/2021/formulas/physics/high-school/fwr3hoc4pnfjn60ezt4ev61l6wzvfomcr0.png)
The horizontal distance is
![d = 1250 \ m](https://img.qammunity.org/2021/formulas/physics/high-school/o34hw824askczljmrw6f41x8t2vusyehx6.png)
Generally the time taken by the hot magma in air before landing is mathematically represented as
![t = (d)/(u_x)](https://img.qammunity.org/2021/formulas/physics/high-school/rziawstgm6bg6d2wt8ytow5dq9dybvrd00.png)
=>
![t = ( 1250 )/(252)](https://img.qammunity.org/2021/formulas/physics/high-school/hbw4o5v74hfdbjleczb7cgs1ep885ispgt.png)
=>
![t = 4.96 \ s](https://img.qammunity.org/2021/formulas/physics/high-school/udkvbrycofixn0a71429q8oofufeywe3s1.png)
Generally the initial vertical velocity of the magma when it was lunched is
![u_y = 0 \ m/ s](https://img.qammunity.org/2021/formulas/physics/high-school/c3v2fwuv5zma8p4ur3altl5lsnwqmwufuj.png)
Then the final velocity of the magma when it hits the ground is mathematically represented s
![- v_y = u_y + gt](https://img.qammunity.org/2021/formulas/physics/high-school/hwt5nkakl9rh6k8q3md62ttr7dpth23gyz.png)
Here the negative sign mean that the direction of the velocity is towards the negative y -axis
So
![- v_y = 48.61 \ m/s](https://img.qammunity.org/2021/formulas/physics/high-school/93gtme3735xf5dmnlbpdp9s8ozb02g6qpz.png)
=>
![v_y = -48.61 \ m/s](https://img.qammunity.org/2021/formulas/physics/high-school/oi4mc6oqumk5ofsq6em706plb7kyaol9pw.png)