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Class 11 NEET Physics System of Particles and Rotational Motion
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© examsnet.com
Question : 54
Total: 109
A small mass attached to a string rotates on a frictionless table top as shown. If the tension in the string is increased by pulling the string causing the radius of the circular motion to decrease by a factor of 2, the kinetic energy of the mass will
(2011 Mains)
decrease by a factor of 2
remain constant
increase by a factor of 2
increase by a factor of 4
Validate
Solution:
According to law of conservation of angular momentum
m
v
r
=
m
v
′
r
′
v
r
=
v
′
(
r
2
)
v
′
=
2
v
..........(i)
∴
K
K
′
=
1
2
m
v
2
1
2
m
v
′
2
(
v
v
′
)
2
or
K
′
K
=
(
v
′
v
)
2
=
(
2
)
2
(Using (i))
K
′
=
4
K
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