1
JEE Main 2019 (Online) 10th April Evening Slot
MCQ (Single Correct Answer)
+4
-1
A metal coin of mass 5 g and radius 1 cm is fixed to a thin stick AB of negligible mass as shown in the figure. The system is initially at rest. The constant torque, that will make the system rotate about AB at 25 rotations per second in 5s, is close to :
A
7.9 × 10–6 Nm
B
4.0 × 10–6 Nm
C
2.0 × 10–5 Nm
D
1.6 × 10–5 Nm
2
JEE Main 2019 (Online) 10th April Morning Slot
MCQ (Single Correct Answer)
+4
-1
Two coaxial discs, having moments of inertia I1 and I1/2, are rotating with respective angular velocities $$\omega$$1 and $$\omega$$1/2 , about their common axis. They are brought in contact with each other and thereafter they rotate with a common angular velocity. If Ef and Ei are the final and initial total energies, then (Ef - Ei) is:
A
$${{{I_1}\omega _1^2} \over {24}}$$
B
$${{{I_1}\omega _1^2} \over {12}}$$
C
$${3 \over 8}{I_1}\omega _1^2$$
D
$${{{I_1}\omega _1^2} \over {6}}$$
3
JEE Main 2019 (Online) 9th April Evening Slot
MCQ (Single Correct Answer)
+4
-1
Moment of inertia of a body about a given axis is 1.5 kg m2. Initially the body is at rest. In order to produce a rotational kinetic energy of 1200 J, the angular accleration of 20 rad/s2 must be applied about the axis for a duration of :-
A
2.5 s
B
3 s
C
5s
D
2 s
4
JEE Main 2019 (Online) 9th April Evening Slot
MCQ (Single Correct Answer)
+4
-1
A thin smooth rod of length L and mass M is rotating freely with angular speed $$\omega$$0 about an axis perpendicular to the rod and passing through its center. Two beads of mass m and negligible size are at the center of the rod initially. The beads are free to slide along the rod. The angular speed of the system , when the beads reach the opposite ends of the rod, will be :-
A
$${{M{\omega _0}} \over {M + 3m}}$$
B
$${{M{\omega _0}} \over {M + m}}$$
C
$${{M{\omega _0}} \over {M + 6m}}$$
D
$${{M{\omega _0}} \over {M + 2m}}$$
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