Hey pls don’t. Report my answer I’m in a test and I rlly want someone to answer my question
The focal length, like you said it's the distance between the FOCAL point and the mirror.
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
Explanation :
When a person is sliding with constant velocity, the forces that are acting on him are :
(1) Weight, W = mg where g is acceleration due to gravity.
(2) Friction forces acting opposite to the direction of motion.
(3) Normal force.
The forces acting on the person is balanced because the person is sliding with constant velocity.
From figure it is clear that, friction force is balanced by
and normal is balanced by
.