Elastic potential energy =21.Y.(LΔl)2AL
=21Y.(0.420.2)2.(π×32×10−6×0.42)
=(1.35×10−6)Y
Kinetic energy =21mv2=21×(0.02×(20)2)
(1.35×10−6)Y=4
Y=3×106Nm−2
A boy’s catapult is made of rubber cord which is 42cm long, with 6mm diameter of cross-section and of negligible mass. The boy keeps a stone weighing 0.02kg on it and stretches the cord by 20cm by applying a constant force. When released, the stone flies off with a velocity of 20ms−1 . Neglect the change in the area of cross-section of the cord while stretched. The Young’s modulus of rubber is closest to:
Held on 8 Apr 2019 · Verified 6 Jul 2026.
106Nm−2
104Nm−2
108Nm−2
103Nm−2
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