To calculate the ideal mechanical advantage of a lever divide the input arm by the output arm.
Mechanical advantage is the amount by which a machine can multiply an input force, calculated by dividing output Force in newtons by input force in newtons, while the ideal mechanical advantage is the mechanical advantage of a machine that has no friction, calculated by dividing the input distance by the output distance.
The simplest answer would be "acceleration due to gravity."
The exact value of this acceleration changes depending on which planet your on (for example).
Explanation:
Given
initial velocity(v_0)=1.72 m/s
using 
Where v=final velocity (Here v=0)
u=initial velocity(1.72 m/s)
a=acceleration 
s=distance traveled
s=0.214 m
(b)time taken to travel 0.214 m
v=u+at
t=0.249 s
(c)Speed of the block at bottom
Here u=0 as it started coming downward
v=1.72 m/s
