1
JEE Advanced 2016 Paper 2 Offline
+3
-0
A frame of the reference that is accelerated with respect to an inertial frame of reference is called a non-inertial frame of reference. A coordinate system fixed on a circular disc rotating about a fixed axis with a constant angular velocity $$\omega$$ is an example of a non-inertial frame of reference. The relationship between the force $$\overrightarrow F$$rot experienced by a particle of mass m moving on the rotating disc and the force $$\overrightarrow F$$in experienced by the particle in an inertial frame of reference is,

$$\overrightarrow F$$rot = $$\overrightarrow F$$in + 2m ($$\overrightarrow v$$rot $$\times$$ $$\overrightarrow \omega$$) + m ($$\overrightarrow \omega$$ $$\times$$ $$\overrightarrow r$$) $$\times$$ $$\overrightarrow \omega$$,

where, vrot is the velocity of the particle in the rotating frame of reference and r is the position vector of the particle with respect to the centre of the disc.

Now, consider a smooth slot along a diameter of a disc of radius R rotating counter-clockwise with a constant angular speed $$\omega$$ about its vertical axis through its centre. We assign a coordinate system with the origin at the centre of the disc, the X-axis along the slot, the Y-axis perpendicular to the slot and the Z-axis along the rotation axis ($$\omega$$ = $$\omega$$ $$\widehat k$$). A small block of mass m is gently placed in the slot at r = (R/2)$$\widehat i$$ at t = 0 and is constrained to move only along the slot.

The net reaction of the disc on the block is
A
$$m{\omega ^2}R\sin \omega t\widehat j - mg\widehat k$$
B
$${1 \over 2}m{\omega ^2}R({e^{\omega t}} - {e^{ - \omega t}})\widehat j + mg\widehat k$$
C
$${1 \over 2}m{\omega ^2}R({e^{2\omega t}} - {e^{ - 2\omega t}})\widehat j + mg\widehat k$$
D
$$- m{\omega ^2}R\cos \omega r\widehat j - mg\widehat k$$
2
JEE Advanced 2016 Paper 1 Offline
+3
-1
A uniform wooden stick of mass 1.6 kg and length $$l$$ rests in an inclined manner on a smooth, vertical wall of height h ( < $$l$$ ) such that a small portion of the stick extends beyond the wall. The reaction force of the wall on the stick is perpendicular to the stick. The stick makes an angle of $$30^\circ$$ with the wall and the bottom of the stick is on a rough floor. The reaction of the wall on the stick is equal in magnitude to the reaction of the floor on the stick. The ratio $${h \over l}$$ and the frictional force f at the bottom of the stick are ( g =10 ms-2 )
A
$${h \over l} = {{\sqrt 3 } \over {16}},f = {{16\sqrt 3 } \over 3}N$$
B
$${h \over l} = {3 \over {16}},f = {{16\sqrt 3 } \over 3}N$$
C
$${h \over l} = {{3\sqrt 3 } \over {16}},f = {{8\sqrt 3 } \over 3}N$$
D
$${h \over l} = {{3\sqrt 3 } \over {16}},f = {{16\sqrt 3 } \over 3}N$$
3
IIT-JEE 2012 Paper 2 Offline
+3
-0.75
Two identical discs of same radius R are rotating about their axes in opposite directions with the same constant angular speed $$\omega$$. The discs are in the same horizontal plane. At time t = 0, the points P and Q are facing each other as shown in the figure. The relative speed between the two points P and Q is vr. In one time period (T) of rotation of the discs, vr as a function of time is best represented by
A
B
C
D
4
IIT-JEE 2012 Paper 2 Offline
+3
-0.75
Consider a disc rotating in the horizontal plane with a constant angular speed $$\omega$$ about its centre O. The disc has a shaded region on one side of the diameter and an unshaded region on the other side as shown in the figure. When the disc is in the orientation as shown, two pebbles P and Q are simultaneously projected at an angle towards R. The velocity of projection is in the y - z plane and is same for both pebbles with respect to the disc. Assume that (i) they land back on the disc before the disc has completed $${1 \over 8}$$ rotation, (ii) their range is less than half the disc radius, and (iii) $$\omega$$ remains constant throughout. Then

A
P lands in the shaded region and Q in the unshaded region.
B
P lands in the unshaded region and Q in the shaded region.
C
Both P and Q land in the unshaded region.
D
Both P and Q land in the shaded region.
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