Centre of Mass & Rotational Motion · JEE Main previous year questions

2020 30 questions

1. Q262020 · 8 Jan 2020 · Shift 2
   
   1. A.$(R^2+R-1)(2-R)=1$
   2. B.$(R^2-R-1)(2-R)=1$
   3. C.$(R^2-R+1)(2-R)=1$
   4. D.$(R^2+R+1)(2-R)=1$
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   Answer: D

2. Q302020 · 7 Jan 2020 · Shift 1

   The radius of gyration of a uniform rod of length $l$, about an axis passing through a point $\frac{l}{4}$ away from the centre of the rod, and perpendicular to it, is :

   1. A.$\frac{1}{8}l$
   2. B.$\frac{1}{4}l$
   3. C.$\sqrt{\frac{7}{48}}l$
   4. D.$\sqrt{\frac{3}{8}}l$
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   Answer: C

3. Q412020 · 7 Jan 2020 · Shift 1
   
   1. A.$2.0\mathrm{cm}$ right and $0.9\mathrm{cm}$ above $1\mathrm{kg}$ mass
   2. B.$0.9\mathrm{cm}$ right and $2.0\mathrm{cm}$ above $1\mathrm{kg}$ mass
   3. C.$0.6\mathrm{cm}$ right and $2.0\mathrm{cm}$ above $1\mathrm{kg}$ mass
   4. D.$1.5\mathrm{cm}$ right and $1.2\mathrm{cm}$ above $1\mathrm{kg}$ mass
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   Answer: B

4. Q462020 · 7 Jan 2020 · Shift 1· Numerical answer

   A non-isotropic solid metal cube has coefficients of linear expansion as : $5\times 10^{-5}/{}^{\circ }\mathrm{C}$ along the x-axis and $5\times 10^{-6}/{}^{\circ }\mathrm{C}$ along the y and the z-axis. If the coefficient of volume expansion of the solid is $\mathrm{C}\times 10^{-6}/{}^{\circ }\mathrm{C}$ then the value of C is

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   Answer: 60

5. Q272020 · 7 Jan 2020 · Shift 2

   Mass per unit area of a circular disc of radius $a$ depends on the distance r from its centre as $\sigma (r)=A+Br$. The moment of inertia of the disc about the axis, perpendicular to the plane and passing through its centre is:

   1. A.$2\pi a^4\left(\frac{A}{4}+\frac{aB}{5}\right)$
   2. B.$\pi a^4\left(\frac{A}{4}+\frac{aB}{5}\right)$
   3. C.$2\pi a^4\left(\frac{aA}{4}+\frac{B}{5}\right)$
   4. D.$2\pi a^4\left(\frac{A}{4}+\frac{B}{5}\right)$
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   Answer: A