Question
Wheels of diameters 7 cm and 14 cm start rolling simultaneously from X and Y , which 1980 cm, towards each other in opposite directions . Both of them make the same number of revolutions per second. If both of them meet after 10 second , the speed of the smaller wheel is :
Answer: Option A
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Let each wheel make ` X` revolutions per sec. Then
`[(2 pi xx 7/2 xx X) + (2 pi xx 7 xx X] xx 10` = 1980
`hArr (22/7 xx 7 xx X) + ( 2 xx 22/7 xx 7 xx X) = 198`
`hArr 66 X = 198`
`hArr X = 3`
Distance moved by smaller wheel in 3 revolutions = `(2 xx 22/7 xx 7/2 xx 3)` cm = 66 cm
`:.` Speed of smaller wheel = `66/3` cm./sec = 22 cm/sec.
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