Answer:505.94 N
Explanation:
Given
mass of child (m)=41 kg
N=60 rpm

Radius(r)=1.25 m
and centripetal acceleration is given by 

Here in this question as we can see there is no air friction so we can use the principle of energy conservation


now here we know that



now plug in all values in above equation

divide whole equation by mass "m"



so height of the ball from ground will be 1.35 m
The number and units. An example would be 3cm or 4kg.