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Question: Answered & Verified by Expert
A sphere is rotating between two rough inclined walls as shown in figure. Coefficient of friction between each wall and the sphere is 13. If f1 and f2 be the frictional forces at P and Q. Then f1f2 is

PhysicsRotational MotionJEE Main
Options:
  • A 4 3 + 1
  • B 1 3 + 2
  • C 1 2 + 3
  • D 1 + 2 3
Solution:
2611 Upvotes Verified Answer
The correct answer is: 4 3 + 1
Let μ be the friction coefficient between sphere and each wall. Free body diagram of sphere is



Net force on the sphere in horizontal diarection is zero.
N1cos60ο+μN2cos60ο=N2cos30ο+μN1cos30ο
N1+μN2=3N2+μN1
N11-3μ=N23-μ
N1N2=3-μ1-3μ
Substituting μ=13 we get,
N1N2=3-131-33=33-13-3=1+43
f1f2=μN1μN2=1+43

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