Question

Problem 3 (30 points) 3.1 A rubber band, 5cm long, is stretched uniaxially to 10cm at 25C and is held in this state. The stress at this length is found to increase by 1.2-10 Pa when the temperature is raised to 30°C. Assuming ideal behavior calculate (a) the concentration of elastically active strands; (b) Young's moduļus (E) at 2% ofelongation of the rubber at 25°C (E-o(at 2% of elongation)/0.02) (10 points) 3.2 Stress-strain measurements on lightly vulcanized naturally rubber sample yielded a value of 1.9. 106 Pa fr Young's modulus at low extensions. Calculate the molecular weight of an average effective chain strand between crosslinks. The density of the rubber is 0.94 g/cm. (10 points)Ream Tent 2s 2.4 Suppose you have a balloon made of an ideal elastomer that is inflated to a reasonable size with an ideal gas at room temperature. If the temperature of the balloon and gas increased to 100°c, will the balloon contract, expand or stay the same size. Justify your answer. Assume gas behaves ideally: PV (mgas/Hga) RT (10 points)

Answer 1

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