GATE XE format:nat PYQs & Answers — Page 37

Questions 361–370 of 668. Imported answers require independent review unless marked reviewed.

Topic practice 668 questionsPage 37 of 67

An air-standard Diesel cycle with a compression ratio of 16 takes air at 1 bar and 300 K. If the maximum temperature in the cycle is 2100 K, then the thermal efficiency of the cycle is ______ % (1 decimal place). The ratio of the specific heat capacities of air is 1.4.

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The plateau modulus of polystyrene has a value of 0.2 × 10⁶ Pa at 150 °C. Given, the density of polystyrene is 1.05 g/cm³, the universal gas constant,

= 8.3 J K⁻¹ mol⁻¹, and the monomer molecular weight is 104 g/mol. The molecular weight between entanglements (rounded off to the nearest integer) of polystyrene chains is ______ g/mol.

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A unidirectional composite of epoxy and carbon fiber of 50% by volume is made. The elastic modulus of epoxy and carbon fiber are 3.5 GPa and 350 GPa, respectively. The ratio (rounded off to one decimal place) of the modulus of the composite to the matrix modulus is ______.

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A single screw extruder is operating at a rotational speed of 2 revolutions per second for the extrusion of a Newtonian polymer under open-discharge conditions (in absence of a die, the pressure drop,

= 0). The extruder has a screw diameter,

= 5 cm, a channel depth,

= 0.4 cm, distance between flights,

= 1 cm, and a helix angle,

= 20°. Assume the value of

= 3.14. The volumetric flow rate (rounded off to 2 decimal places) is ______ cm³/s.

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At 215 °C, the viscosity of a polystyrene of molecular weight 250 × 10³ g/mol is 8.0 × 10³ Pa s. The critical molecular weight of polystyrene,

= 35 × 10³ g/mol. For a similar polystyrene of molecular weight 500 × 10³ g/mol, the viscosity (rounded off to nearest integer) will be ______ × 10³ Pa s.

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There are two different PTFE polymer specimens of the following density (

) and % crystallinity. For PTFE- specimen-1,

is 2.144 g/cm³ and % crystallinity is 50. For PTFE- specimen-2,

is 2.215 g/cm³ and % crystallinity is 75. Assuming the polymer is pure and defect free, the density (rounded off to 3 decimal places) of 100% amorphous PTFE specimen will be ______ g/cm³.

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The behavior of a polymer is described by a Maxwell model consisting of a spring element of modulus 10¹⁰ Pa in series with a dashpot of viscosity 10¹² Pa s. In the solid, 50 s after the sudden application of a fixed strain of 1%, the stress (rounded off to 2 decimal places) will be ______ × 10⁷ Pa.

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A particular free radical polymerization process yields a polymer with a number average degree of polymerization,

= 100. The monomer concentration is doubled and the initiator concentration is increased by four times. Assuming that all rate coefficients and other parameters remain unchanged, the value of

(rounded off to the nearest integer) is ______.

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A polymer is synthesized from 2 moles of terephthalic acid (molecular weight of the repeat unit, (-OCC₆H₄CO-), is 132 g/mol), 1 mol of ethylene glycol (molecular weight of the repeat unit, (-OCH₂CH₂O-), is 60 g/mol), and 1 mol of butylene glycol (molecular weight of the repeat unit, (-O(CH₂)₄O-), is 88 g/mol). The reaction is terminated at 99% conversion of the acid. The number averaged molecular weight,

(rounded off to the nearest integer) is ______ g/mol.

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A sample of natural rubber (cis-1,4-polyisoprene) is vulcanized such that one of every 240 chain carbon atoms is cross-linked. The formula unit of the isoprene monomer is C₅H₈ (molecular weight = 68 g/mol). The average molecular weight (rounded off to the nearest integer) between cross-links is ______ g/mol.

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GATE XE format:nat PYQs

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