1
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.
2
JEE Main 2021 (Online) 24th February Evening Shift
+4
-1
A circular hole of radius $$\left( {{a \over 2}} \right)$$ is cut out of a circular disc of radius 'a' as shown in figure. The centroid of the remaining circular portion with respect to point 'O' will be :

A
$${1 \over 6}a$$
B
$${2 \over 3}a$$
C
$${5 \over 6}a$$
D
$${10 \over 11}a$$
3
JEE Main 2020 (Online) 6th September Evening Slot
+4
-1
Particle A of mass m1 moving with velocity $$\left( {\sqrt3\widehat i + \widehat j} \right)m{s^{ - 1}}$$ collides with another particle B of mass m2 which is at rest initially. Let $$\overrightarrow {{V_1}}$$ and $$\overrightarrow {{V_2}}$$ be the velocities of particles A and B after collision respectively. If m1 = 2m2 and after
collision $$\overrightarrow {{V_1}} =$$$$\left( {\widehat i + \sqrt 3 \widehat j} \right)$$ , the angle between $$\overrightarrow {{V_1}}$$ and $$\overrightarrow {{V_2}}$$ is :
A
105o
B
15o
C
-45o
D
60o
4
JEE Main 2020 (Online) 4th September Morning Slot
+4
-1
Blocks of masses m, 2m, 4m and 8m are arranged in a line on a frictionless floor. Another block of mass m, moving with speed v along the same line (see figure) collides with mass m in perfectly inelastic manner. All the subsequent collisions are also perfectly inelastic. By the time the last block of mass 8m starts moving the total energy loss is p% of the original energy. Value of 'p' is close to :
A
37
B
77
C
87
D
94
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