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JEE Main Physics Class 11 Laws Of Motion Part 1 Questions
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© examsnet.com
Question : 13
Total: 100
The boxes of masses
2
kg
and
8
kg
are connected by a massless string passing over smooth pulleys. Calculate the time taken by box of mass
8
kg
to strike the ground starting from rest.
(Use,
g
=
10
m
∕
s
2
)
[27 Aug 2021 Shift 2]
0.34 s
0.2 s
0.25 s
0.4 s
Validate
Solution:
According to the given figure, and free body diagram
masses of two bodies
m
1
=
2
k
g
m
2
=
8
k
g
,
Acceleration of mass
m
1
=
a
Acceleration of mass
m
2
=
a
2
Tension
=
T
Distance between
m
2
and ground
=
20
c
m
=
0.2
m
Initial velocity
u
=
0
Equation of motion of
2
k
g
block,
∴
T
−
2
g
=
2
a
⋅
⋅
⋅
⋅
⋅
⋅
⋅
(
i
)
Equation of motion of
8
k
g
block, and
8
g
−
2
T
=
8
a
2
⇒
4
g
−
T
=
2
a
⋅
⋅
⋅
⋅
⋅
⋅
⋅
(
i
i
)
From Eqs. (i) and (ii),
⇒
T
−
2
g
=
4
g
−
T
Substituting the value in Eq. (i) we get
3
g
−
2
g
=
2
a
⇒
g
=
2
a
⇒
a
=
g
2
=
5
m
s
−
2
∴
a
1
=
5
m
s
−
2
and
2
=
5
2
m
s
−
2
Since,
s
=
u
t
+
1
2
a
t
2
∴
20
100
=
0
+
1
2
5
2
×
t
2
⇒
t
2
=
20
×
4
5
×
100
⇒
t
=
2
5
=
0.4
s
© examsnet.com
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