How Much Work Was Done By The Person Who Pulled The Cord?

F=mv^2/r
F= centripetal force towards center
m=mass
v=velocity
r=radius
 
F1=mv1^2/r1
F1=((0.120)(0.7)^2)/(0.4)=0.147 newton
 
F2=mv2^2/r2
F2=((0.120)(2.8)^2)/(0.1)=9.402
 
net force=F2-F1=9.261
net distance= 0.4-0.1=0.3
 
work done=Force * distance= 9.261* 0.3= 2.7783