Potential energy stored in the rubber cord catault will be converted into kinetic energy of mass
2
1
mv
2
=
2
1
L
YAl
2
where l=5×10
−2
m, A=25×10
−6
m
2
, L=10×10
−2
m, m=5×10
−3
kg
⇒v=
mL
YAl
2
v=
5×10
−3
×10×10
−2
5×10
8
×25×10
−6
×(5×10
−2
)
2
v=250ms
−1
