1
JEE Main 2021 (Online) 25th July Morning Shift
+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
$$Y = {{{Y_1}{Y_2}} \over {{Y_1} + {Y_2}}}$$
2
JEE Main 2021 (Online) 20th July Evening Shift
+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
$${{{l_1} + {l_2}} \over 2}$$
3
JEE Main 2021 (Online) 20th July Evening Shift
+4
-1
Two small drops of mercury each of radius R coalesce to form a single large drop. The ratio of total surface energy before and after the change is :
A
$${2^{{1 \over 3}}}:1$$
B
$$1:{2^{{1 \over 3}}}$$
C
2 : 1
D
1 : 2
4
JEE Main 2021 (Online) 20th July Morning Shift
+4
-1
The value of tension in a long thin metal wire has been changed from T1 to T2. The lengths of the metal wire at two different values of tension T1 and T2 are l1 and l2 respectively. The actual length of the metal wire is :
A
$${{{l_1} + {l_2}} \over 2}$$
B
$$\sqrt {{T_1}{T_2}{l_1}{l_2}}$$
C
$${{{T_1}{l_2} - {T_2}{l_1}} \over {{T_1} - {T_2}}}$$
D
$${{{T_1}{l_1} - {T_2}{l_2}} \over {{T_1} - {T_2}}}$$
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