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A boy’s catapult is made of rubber cord which is 42 cm long, with 6 mm diameter of cross-section and of negligible mass. The boy keeps a stone weighing 0.02 kg on it and stretches the cord by 20 cm by applying a constant force. When released, the stone flies off with a velocity of 20 ms –1 . Neglect the change in the area of cross-section of the cord while stretched. The Young’s modulus of rubber is closest to -

1. 10 3 Nm –2
2. 10 4 Nm –2
3. 10 6 Nm –2
4. 10 8 Nm –2

Correct answer: 10 6 Nm –2

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