As per Newton's II law we know that

here
F = applied unbalanced force
m = mass of object
a = acceleration of object
now it is given that force F = 50 N North applied on block on earth due to which block will accelerate by 4 m/s^2
so here from above equation


Now we took another situation where block is placed on surface of moon and again force F = 25 N is applied on the block
So we will again use Newton's II law




so block will accelerate on moon by acceleration 2 m/s^2
Sound waves are known to be the one that's not considered as a type of electromagnetic energy. As for microwaves and x-rays, they tend to share the same frequencies that can be considered as electromagnetic, and sound waves have a different frequency than them.
Answer:
60 m/s (in the opposite direction)
Explanation:
By conservation of momentum,
Initial momentum of board + Initial momentum of man = Final momentum of board + Final momentum of man
=> 0 + 40*12 = 8*(-v) + 0
=> v = -60 [ Negative indicates opposite direction ]