1
JEE Main 2019 (Online) 11th January Morning Slot
+4
-1
A slab is subjected to two forces $$\overrightarrow {{F_1}}$$ and $$\overrightarrow {{F_2}}$$ of same magnitude F as shown in the figure. Force $$\overrightarrow {{F_2}}$$ is in XY-plane while force $$\overrightarrow {{F_1}}$$ acts along z = axis at the point $$\left( {2\overrightarrow i + 3\overrightarrow j } \right).$$. The moment of these forces about point O will be : A
$$\left( {3\widehat i - 2\widehat j - 3\widehat k} \right)F$$
B
$$\left( {3\widehat i + 2\widehat j - 3\widehat k} \right)F$$
C
$$\left( {3\widehat i + 2\widehat j + 3\widehat k} \right)F$$
D
$$\left( {3\widehat i - 2\widehat j + 3\widehat k} \right)F$$
2
JEE Main 2019 (Online) 11th January Morning Slot
+4
-1
An equilateral triangle ABC is cut from a thin solid sheet of wood. (see figure) D, E and F are the mid-points of its sides as shown and G is the centre of the triangle. The moment of inertia of the triangle about an axis passing through G and perpendicular to the plane of the triangle is I0. If the smaller triangle DEF is removed from ABC, the moment of inertia of the remaining figure about the same axis is I. then : A
$${\rm I} = {{{{\rm I}_0}} \over 4}$$
B
$${\rm I} = {{15} \over {16}}{{\rm I}_0}$$
C
$${\rm I} = {9 \over {16}}{{\rm I}_0}$$
D
$${\rm I} = {3 \over 4}{{\rm I}_0}$$
3
JEE Main 2019 (Online) 10th January Evening Slot
+4
-1
Two identical spherical balls of mass M and radius R each are stuck on two ends of a rod of length 2R and mass M (see figure). The moment of inertia of the system about the axis passing perpendicularly through the centre of the rod is : A
$${{17} \over {15}}$$ MR2
B
$${{137} \over {15}}$$ MR2
C
$${{209} \over {15}}$$ MR2
D
$${{152} \over {15}}$$ MR2
4
JEE Main 2019 (Online) 10th January Morning Slot
+4
-1
To mop-clean a floor, a cleaning machine presses a circular mop of radius R vertically down with a total force F and rotates it with a constant angular speed about its axis. If the force F is distributed uniformly over the mop and if coefficient of friction between the mop and the floor is $$\mu$$, the torque, applied by the machine on the mop is -
A
$$\mu$$FR/2
B
$$\mu$$FR/3
C
$$\mu$$FR/6
D
$${2 \over 3}$$$$\mu$$FR
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