1
JEE Main 2021 (Online) 17th March Evening Shift
+4
-1
Two identical blocks A and B each of mass m resting on the smooth horizontal floor are connected by a light spring of natural length L and spring constant K. A third block C of mass m moving with a speed v along the line joining A and B collides with A. The maximum compression in the spring is

A
$$\sqrt {{{mv} \over K}}$$
B
$$\sqrt {{m \over {2K}}}$$
C
$$\sqrt {{{mv} \over {2K}}}$$
D
$$v\sqrt {{m \over {2K}}}$$
2
JEE Main 2021 (Online) 16th March Evening Shift
+4
-1
A large block of wood of mass M = 5.99 kg is hanging from two long massless cords. A bullet of mass m = 10 g is fired into the block and gets embedded in it. The (block + bullet) then swing upwards, their centre of mass rising a vertical distance h = 9.8 cm before the (block + bullet) pendulum comes momentarily to rest at the end of its arc. The speed of the bullet just before collision is :
(take g = 9.8 ms-2)

A
831.4 m/s
B
811.4 m/s
C
841.4 m/s
D
821.4 m/s
3
JEE Main 2021 (Online) 16th March Morning Shift
+4
-1
Four equal masses, m each are placed at the comers of a square of length (l) as shown in the figure. The moment of inertia of the system about an axis passing through A and parallel to DB would be :

A
$$\sqrt 3$$ ml2
B
2 ml2
C
ml2
D
3 ml2
4
JEE Main 2021 (Online) 26th February Morning Shift
+4
-1
Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R.

Assertion A : Body 'P' having mass M moving with speed 'u' has head-on collision elastically with another body 'Q' having mass 'm' initially at rest. If m << M, body 'Q' will have a maximum speed equal to '2u' after collision.

Reason R : During elastic collision, the momentum and kinetic energy are both conserved.

In the light of the above statements, choose the most appropriate answer from the options given below :
A
A is correct but R is not correct.
B
A is not correct but R is correct.
C
Both A and R are correct and R is the correct explanation of A.
D
Both A and R are correct but R is NOT the correct explanation of A.
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