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JEE Advanced Model Paper 8 with solutions for online practice
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© examsnet.com
Question : 80
Total: 84
A solid sphere of mass ‘m’ and radius ‘R’ is kept on a rough surface. The velocities of air(density ρ ) around the sphere area as shown in the figure. Assuming ‘R’ to be small and m =
4
π
ρ
R
2
g
kg , the minimum value of coefficient of friction so that the sphere starts pure rolling is
1
β
. (Assuming force due to pressure difference is acting on the centre of mass of the sphere).Determine the value of 'β'
Your Answer:
Validate
Solution:
Force due to pressure difference is F = P × A
=
1
2
ρ
(
V
2
2
−
V
1
2
)
× π
R
2
F =
1
2
ρ
(14 - 7) × π
R
2
=
7
π
ρ
R
2
2
For translational motion F = f = ma .....(1)
For rotational motion
f × R = Iα =
I
a
R
f =
I
a
R
2
=
2
5
m
R
2
×
a
R
2
=
2
5
ma
F = ma + f = ma +
2
5
ma =
7
5
ma
ma =
5
7
F
f =
2
5
×
5
7
F =
2
F
7
=
2
7
×
7
π
ρ
R
2
2
f = πρ
R
2
µMg = πρ
R
2
µ
π
ρ
R
2
m
g
=
1
4
⇒ µ =
1
4
=
1
β
⇒ β = 4
© examsnet.com
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