1
JEE Main 2020 (Online) 3rd September Morning Slot
+4
-1
Moment of inertia of a cylinder of mass M, length L and radius R about an axis passing through its centre and perpendicular to the axis of the cylinder is
I = $$M\left( {{{{R^2}} \over 4} + {{{L^2}} \over {12}}} \right)$$. If such a cylinder is to be made for a given mass of a material, the ratio $${L \over R}$$ for it to have minimum possible I is
A
$${3 \over 2}$$
B
$$\sqrt {{3 \over 2}}$$
C
$$\sqrt {{2 \over 3}}$$
D
$${{2 \over 3}}$$
2
JEE Main 2020 (Online) 2nd September Evening Slot
+4
-1
Two uniform circular discs are rotating independently in the same direction around their common axis passing through their centres. The moment of inertia and angular velocity of the first disc are 0.1 kg-m2 and 10 rad s–1 respectively while those for the second one are 0.2 kg-m2 and 5 rad s–1 respectively. At some instant they get stuck together and start rotating as a single system about their common axis with some angular speed. The kinetic energy of the combined system is :
A
$${{20} \over 3}J$$
B
$${{5} \over 3}J$$
C
$${{10} \over 3}J$$
D
$${{2} \over 3}J$$
3
JEE Main 2020 (Online) 2nd September Morning Slot
+4
-1
A bead of mass m stays at point P(a, b) on a wire bent in the shape of a parabola y = 4Cx2 and rotating with angular speed $$\omega$$ (see figure). The value of $$\omega$$ is (neglect friction) : A
$$2\sqrt {2gC}$$
B
$$2\sqrt {gC}$$
C
$$\sqrt {{{2gC} \over {ab}}}$$
D
$$\sqrt {{{2g} \over C}}$$
4
JEE Main 2020 (Online) 2nd September Morning Slot
+4
-1 Shown in the figure is rigid and uniform one meter long rod AB held in horizontal position by two strings tied to its ends and attached to the ceiling. The rod is of mass ‘m’ and has another weight of mass 2 m hung at a distance of 75 cm from A. The tension in the string at A is :
A
0.5 mg
B
2 mg
C
0.75 mg
D
1 mg
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