1
JEE Main 2021 (Online) 27th July Morning Shift
MCQ (Single Correct Answer)
+4
-1
Out of Syllabus
A body takes 4 min. to cool from 61$$^\circ$$ C to 59$$^\circ$$ C. If the temperature of the surroundings is 30$$^\circ$$ C, the time taken by the body to cool from 51$$^\circ$$ C to 49$$^\circ$$ C is :
A
4 min.
B
3 min.
C
8 min.
D
6 min.
2
JEE Main 2021 (Online) 25th July Evening Shift
MCQ (Single Correct Answer)
+4
-1
Two spherical soap bubbles of radii r1 and r2 in vacuum combine under isothermal conditions. The resulting bubble has a radius equal to :
A
$${{{r_1}{r_2}} \over {{r_1} + {r_2}}}$$
B
$$\sqrt {{r_1}{r_2}} $$
C
$$\sqrt {r_1^2 + r_2^2} $$
D
$${{{r_1} + {r_2}} \over 2}$$
3
JEE Main 2021 (Online) 25th July Morning Shift
MCQ (Single Correct Answer)
+4
-1
Two wires of same length and radius are joined end to end and loaded. The Young's modulii of the materials of the two wires are Y1 and Y2. The combination behaves as a single wire then its Young's modulus is :
A
$$Y = {{2{Y_1}{Y_2}} \over {3({Y_1} + {Y_2})}}$$
B
$$Y = {{2{Y_1}{Y_2}} \over {{Y_1} + {Y_2}}}$$
C
$$Y = {{{Y_1}{Y_2}} \over {2({Y_1} + {Y_2})}}$$
D
$$Y = {{{Y_1}{Y_2}} \over {{Y_1} + {Y_2}}}$$
4
JEE Main 2021 (Online) 20th July Evening Shift
MCQ (Single Correct Answer)
+4
-1
The length of a metal wire is l1, when the tension in it is T1 and is l2 when the tension is T2. The natural length of the wire is :
A
$$\sqrt {{l_1}{l_2}} $$
B
$${{{l_1}{T_2} - {l_2}{T_1}} \over {{T_2} - {T_1}}}$$
C
$${{{l_1}{T_2} + {l_2}{T_1}} \over {{T_2} + {T_1}}}$$
D
$${{{l_1} + {l_2}} \over 2}$$
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