A disc revolves with a speed 33 3 1 rev ./ min and has a radius of 15 cm . Two coins are placed at 4 cm and 14 cm. away from the centre of the disc. If the coefficient of friction between the coins

Question

A disc revolves with a speed 33 3 1 ​ rev ./ min and has a radius of 15 cm . Two coins are placed at 4 cm and 14 cm. away from the centre of the disc. If the coefficient of friction between the coins and the disc is 0.15. Coin placed at x cm will not revolve with record. Find x :-

TestHub · Accepted Answer

Coin will revolve with record if μ mg ≥ m 2 r ⇒ μ g ≥ ω 2 r For coin placed at 4 cm μ g = ( 0.15 ) ( 10 ) = 1.5 , ω 2 r = ( 2 π × 3 × 60 100 ​ ) 2 ( 4 × 1 0 − 2 ) = 0.5 ⇒ μ g > ω 2 r ⇒ revolve with record For coin placed at 14 cm ω 2 r = ( 2 π × 3 × 60 100 ​ ) 2 ( 14 × 1 0 − 2 ) = 1.75 ⇒ μ g < ω 2 r ⇒ does not revolve with record

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