1
JEE Main 2020 (Online) 5th September Evening Slot
MCQ (Single Correct Answer)
+4
-1
A radioactive nucleus decays by two different processes. The half life for the first process is 10 s and that for the second is 100 s. The effective half life of the nucleus is close to :
A
12 sec
B
9 sec
C
55 sec
D
6 sec
2
JEE Main 2020 (Online) 5th September Morning Slot
MCQ (Single Correct Answer)
+4
-1
Activities of three radioactive substances A, B and C are represented by the curves A, B and C, in the figure. Then their half-lives
$${T_{{1 \over 2}}}\left( A \right)$$ : $${T_{{1 \over 2}}}\left( B \right)$$ : $${T_{{1 \over 2}}}\left( C \right)$$ are in the ratio :
A
3 : 2 : 1
B
2 : 1 : 1
C
4 : 3 : 1
D
2 : 1 : 3
3
JEE Main 2020 (Online) 3rd September Evening Slot
MCQ (Single Correct Answer)
+4
-1
The radius R of a nucleus of mass number A can be estimated by the formula
R = (1.3 $$\times$$ 10–15)A1/3 m.
It follows that the mass density of a nucleus is of the order of :

(Mprot. $$\cong$$ Mneut $$\simeq$$ 1.67 $$\times$$ 10–27 kg)
A
1024 kg m–3
B
1010 kg m–3
C
1017 kg m–3
D
103 kg m–3
4
JEE Main 2020 (Online) 3rd September Evening Slot
MCQ (Single Correct Answer)
+4
-1
Hydrogen ion and singly ionized helium atom are accelerated, from rest, through the same potential difference. The ratio of final speeds of hydrogen and helium ions is close to :
A
2 : 1
B
1 : 2
C
5 : 7
D
10 : 7
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