A stone of mass 20 g is projected from a rubber catapult of length 0.1 m and area of cross section $10 ^ { - 6 } \mathrm {~m} ^ { 2 }$ stretched by an amount 0.04 m. The velocity of the projected stone is $\mathrm { m } \mathrm { s} ^ { - 1 }$. (Young's modulus of rubber $= 0.5 \times 10 ^ { 9 } \mathrm {~N} \mathrm {~m} ^ { - 2 }$)