1
JEE Main 2021 (Online) 27th July Evening Shift
+4
-1
A raindrop with radius R = 0.2 mm falls from a cloud at a height h = 2000 m above the ground. Assume that the drop is spherical throughout its fall and the force of buoyance may be neglected, then the terminal speed attained by the raindrop is :

[Density of water fw = 1000 kg m$$-$$3 and Density of air fa = 1.2 kg m$$-$$3, g = 10 m/s2, Coefficient of viscosity of air = 1.8 $$\times$$ 10$$-$$5 Nsm$$-$$2]
A
250.6 ms$$-$$1
B
43.56 ms$$-$$1
C
4.94 ms$$-$$1
D
14.4 ms$$-$$1
2
JEE Main 2021 (Online) 27th July Morning Shift
+4
-1
A light cylindrical vessel is kept on a horizontal surface. Area of base is A. A hole of cross-sectional area 'a' is made just at its bottom side. The minimum coefficient of friction necessary to prevent sliding the vessel due to the impact force of the emerging liquid is (a < < A) :

A
$${A \over {2a}}$$
B
None of these
C
$${{2a} \over A}$$
D
$${{a} \over A}$$
3
JEE Main 2021 (Online) 27th July Morning Shift
+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.
4
JEE Main 2021 (Online) 25th July Evening Shift
+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
$${{{r_1} + {r_2}} \over 2}$$
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