1
JEE Main 2020 (Online) 7th January Morning Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
JEE Main 2020 (Online) 7th January Morning Slot Physics - Rotational Motion Question 131 English As shown in the figure, a bob of mass m is tied by a massless string whose other end portion is wound on a fly wheel (disc) of radius r and mass m. When released from rest the bob starts falling vertically. When it has covered a distance of h, the angular speed of the wheel will be:
A
$$r\sqrt {{3 \over {2gh}}} $$
B
$$r\sqrt {{3 \over {4gh}}} $$
C
$${1 \over r}\sqrt {{{4gh} \over 3}} $$
D
$${1 \over r}\sqrt {{{2gh} \over 3}} $$
2
JEE Main 2020 (Online) 7th January Morning Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
If we need a magnification of 375 from a compound microscope of tube length 150 mm and an objective of focal length 5 mm, the focal length of the eye-piece, should be close to :
A
22 mm
B
12 mm
C
33 mm
D
2 mm
3
JEE Main 2020 (Online) 7th January Morning Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
A LCR circuit behaves like a damped harmonic oscillator. Comparing it with a physical spring-mass damped oscillator having damping constant 'b', the correct equivalence would be:
A
L $$ \leftrightarrow $$ k, C $$ \leftrightarrow $$ b, R $$ \leftrightarrow $$ m
B
L $$ \leftrightarrow $$ m, C $$ \leftrightarrow $$ k, R $$ \leftrightarrow $$ b
C
L $$ \leftrightarrow $$ m, C $$ \leftrightarrow $$ $${1 \over k}$$, R $$ \leftrightarrow $$ b
D
L $$ \leftrightarrow $$ $${1 \over b}$$, C $$ \leftrightarrow $$ $${1 \over m}$$, R $$ \leftrightarrow $$ $${1 \over k}$$
4
JEE Main 2020 (Online) 7th January Morning Slot
MCQ (Single Correct Answer)
+4
-1
Change Language
A satellite of mass m is launched vertically upwards with an initial speed u from the surface of the earth. After it reaches height R (R = radius of the earth), it ejects a rocket of mass $${m \over {10}}$$ so that subsequently the satellite moves in a circular orbit. The kinetic energy of the rocket is (G is the gravitational constant; M is the mass of the earth) :
A
$${{3m} \over 8}{\left( {u + \sqrt {{{5GM} \over {6R}}} } \right)^2}$$
B
$${m \over {20}}\left( {{u^2} + {{113} \over {100}}{{GM} \over R}} \right)$$
C
$$5m\left( {{u^2} - {{119} \over {100}}{{GM} \over R}} \right)$$
D
$${m \over {20}}{\left( {u - \sqrt {{{2GM} \over {3R}}} } \right)^2}$$
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