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phy_11_ch_9

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Question 9.1: A steel wire of length 4.7 m and cross-sectional area 3.0 × 10–5 m2 stretches by the same amount as a copper wire of length 3.5 m and cross-sectional area of 4.0 × 10–5 m2 under a given load. What is the ratio of the Young’s modulus of steel to that of copper? Answer Length of the steel wire, L1 = 4.7 m Area of cross-section of the steel wire, A1 = 3.0 × 10–5 m2 Length of the copper wire, L2 = 3.5 m Area of cross-section of the copper wire, A2 = 4.0 × 10–5 m2 Change in length = ΔL
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  Question 9.1:A steel wire of length 4.7 m and cross-sectional area 3.0 × 10  –5 m 2 stretches by the same amount as a copper wire of length 3.5 m and cross-sectional area of 4.0 × 10  –5 m 2 under a given load. What is the ratio of the Young’s modulus of steel to that of copper? Answer Length of the steel wire,  L 1 = 4.7 mArea of cross-section of the steel wire,  A 1 = 3.0 × 10  –5 m 2 Length of the copper wire,  L 2 = 3.5 mArea of cross-section of the copper wire,  A 2 = 4.0 × 10  –5 m 2 Change in length = Δ  L 1 = Δ  L 2 = Δ  L Force applied in both the cases =  F  Young’s modulus of the steel wire:… ( i )Young’s modulus of the copper wire:Dividing ( i ) by ( ii ), we get:  The ratio of Young’s modul Question 9.2:Figure 9.11 shows the strain-modulus and (b) approximat Answer It is clear from the given gra ∴ Young’s modulus, Y  Hence, Young’s modulus for The yield strength of a mater without crossing the elastic lIt is clear from the given gra × 10 6  Nm/ 2 or 3 × 10 8  N/m 2 .Question 9.3: s of steel to that of copper is 1.79 : 1.stress curve for a given material. What are (a) yield strength for this material? h that for stress 150 × 10 6  N/m 2 , strain is 0.002 the given material is 7.5 ×10 10  N/m 2 . ial is the maximum stress that the material can s mit. h that the approximate yield strength of this ma oung’s . ustain terial is 300  The stress-strain graphs for The graphs are drawn to the Which of the materials has t Which of the two is the stron AnswerAnswer: (a) A (b) A For a given strain, the stress the two graphs.Young’s modulus For a given strain, if the stres greater for that material. The for material B .The amount of stress require  point, gives the strength of t strain curve. It can be observ Hence, material A is stronge Question 9.4:Read the following two state false. aterials A and B are shown in Fig. 9.12. ame scale. e greater Young’s modulus? ger material? or material A is more than it is for material B , s for a material is more, then Young’s modulus efore, Young’s modulus for material A is great for fracturing a material, corresponding to its at material. Fracture point is the extreme point   ed that material A can withstand more strain tha than material B . ents below carefully and state, with reasons, i s shown in is also er than it is racture n a stress-n material B . it is true or  The Young’s modulus of rub The stretching of a coil is de AnswerAnswer: (a) False (b) TrueFor a given stress, the strain Young’s modulus,For a constant stress: Hence, Young’s modulus for Shear modulus is the ratio of stretching of a coil changes i this process.Question 9.5:Two wires of diameter 0.25 as shown in Fig. 9.13. The u 1.0 m. Compute the elongati Answer  ber is greater than that of steel; ermined by its shear modulus. n rubber is more than it is in steel. rubber is less than it is for steel. the applied stress to the change in the shape of s shape. Hence, shear modulus of elasticity is i m, one made of steel and the other made of bra loaded length of steel wire is 1.5 m and that of ns of the steel and the brass wires.    a body. The volved in ss are loaded  brass wire is
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