Mathematics MCQs

271

Mathematics • Abstract Algebra

The set of units in Z_14, under the usual operations of addition and multiplication modulo 14, is: The set of units in Z_14, under the usual operations of addition and multiplication modulo 14, is:

A. Z_14 Z_14 B. {1} {1} C. {1, 13, 3, 5, 11, 9} {1, 13, 3, 5, 11, 9} D. {1, -1, 3, 5, 2, 7} {1, -1, 3, 5, 2, 7}

सही उत्तर: C Correct Answer: C

The units modulo 14 are exactly the residue classes relatively prime to 14: 1, 3, 5, 9, 11 and 13.

272

Mathematics • Limits

Calculate lim (x^2 - 4)/(x^2 + 5x - 14) as x approaches 2. Calculate lim (x^2 - 4)/(x^2 + 5x - 14) as x approaches 2.

A. Undefined Undefined B. 2/7 2/7 C. 4/5 4/5 D. 4/9 4/9

सही उत्तर: D Correct Answer: D

Factor and cancel x - 2: (x^2 - 4)/(x^2 + 5x - 14) = (x + 2)/(x + 7). At x = 2 this equals 4/9.

273

Mathematics • Digital Logic

Which logic gate has the following truth table? Inputs (A,B) and output C: (0,0)->0, (0,1)->1, (1,0)->1, (1,1)->1. Which logic gate has the following truth table? Inputs (A,B) and output C: (0,0)->0, (0,1)->1, (1,0)->1, (1,1)->1.

A. OR with 2 inputs OR with 2 inputs B. NAND NAND C. AND with 2 inputs AND with 2 inputs D. NOR NOR

सही उत्तर: A Correct Answer: A

The output is 1 whenever at least one input is 1, which is the truth table of a two-input OR gate.

274

Mathematics • Group Theory

Which one of the following is a group? Which one of the following is a group?

A. The set of all 2 by 2 matrices under multiplication. The set of all 2 by 2 matrices under multiplication. B. (R+, x), where a x b = sqrt(ab) for all a, b in R+. (R+, x), where a x b = sqrt(ab) for all a, b in R+. C. (C[0,1], x), where (f x g)(x) = f(x)g(x). (C[0,1], x), where (f x g)(x) = f(x)g(x). D. The set of odd integers under addition. The set of odd integers under addition.

सही उत्तर: C Correct Answer: C

Option C is the answer marked in the source paper. It represents the stated collection of continuous functions under pointwise multiplication.

275

Mathematics • Dynamics

The moment of inertia of a uniform thin rod of mass M and length L about a perpendicular axis of rotation at its end is: The moment of inertia of a uniform thin rod of mass M and length L about a perpendicular axis of rotation at its end is:

A. (1/8)ML^2 (1/8)ML^2 B. (1/2)ML^2 (1/2)ML^2 C. (1/3)ML^2 (1/3)ML^2 D. (1/4)ML^2 (1/4)ML^2

सही उत्तर: C Correct Answer: C

The moment of inertia of a uniform rod about its centre is ML^2/12. By the parallel-axis theorem, about an end it is ML^2/12 + M(L/2)^2 = ML^2/3.

276

Mathematics • Conic Sections

For what value of m is the line y = mx + 5 tangent to the ellipse represented by 4x^2/9 + y^2/16 = 1? For what value of m is the line y = mx + 5 tangent to the ellipse represented by 4x^2/9 + y^2/16 = 1?

A. 2 2 B. plus or minus 2 plus or minus 2 C. plus or minus 3 plus or minus 3 D. 3 3

सही उत्तर: B Correct Answer: B

For y = mx + c to be tangent to x^2/a^2 + y^2/b^2 = 1, c^2 = a^2m^2 + b^2. Here a^2 = 9/4, b^2 = 16 and c = 5, giving m^2 = 4, so m = plus or minus 2.

277

Mathematics • Number Systems

The binary equivalent of 57 is: The binary equivalent of 57 is:

A. 101111 101111 B. 111001 111001 C. 111000 111000 D. 101010 101010

सही उत्तर: B Correct Answer: B

57 = 32 + 16 + 8 + 1, so its binary representation is 111001.

278

Mathematics • Differential Equations

Which of the following can be reduced to a Clairaut equation? Which of the following can be reduced to a Clairaut equation?

A. y' = e^x + e^y + y^2 y' = e^x + e^y + y^2 B. y' = sin(x) + sin(y) y' = sin(x) + sin(y) C. y = x^4p - p^2x, where p = dy/dx y = x^4p - p^2x, where p = dy/dx D. y = 2xp + y^2p^3, where p = dy/dx y = 2xp + y^2p^3, where p = dy/dx

सही उत्तर: D Correct Answer: D

Option D is the equation marked in the source paper as reducible, after suitable substitution, to Clairaut form.

279

Mathematics • Applied Mechanics

The equation for finding the centre of pressure of a rocket is (where (C_N alpha)_n denotes the normal-force coefficient derivative of the nose): The equation for finding the centre of pressure of a rocket is (where (C_N alpha)_n denotes the normal-force coefficient derivative of the nose):

A. (C_N alpha)_n = 3 (C_N alpha)_n = 3 B. (C_N alpha)_n = 2 (C_N alpha)_n = 2 C. (C_N alpha)_n = 1 (C_N alpha)_n = 1 D. (C_N alpha)_n = 4 (C_N alpha)_n = 4

सही उत्तर: B Correct Answer: B

For the rocket nose contribution used in the centre-of-pressure relation, the normal-force coefficient derivative is 2.

280

Mathematics • Digital Logic

Which is called the universal gate? Which is called the universal gate?

A. AND AND B. OR OR C. NAND NAND D. XNOR XNOR

सही उत्तर: C Correct Answer: C

NAND is a universal gate because every Boolean function can be implemented using NAND gates alone.

Mathematics MCQs

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