Circular gears L and R start to rotate at the same time at the same rate.
Circular gears L and R start to rotate at the same time at the same rate. Gear L makes 10 complete revolutions per minute and gear R makes 30 revolutions per minute. How many seconds after the gears start to rotate will gear R have made exactly 6 more revolutions than gear L?
Answer/Solution
e) 18
Steps/Work
Gear L -- 10 rotations per 60 seconds -- 1 rotation per 6 seconds.
Gear R -- 40 rotations per 60 seconds -- 3 rotations per 6 seconds.
First 6 seconds -- Gear L makes 1 rotation. -- Gear R makes 4 rotations -- Net difference --2 rotations
Hence every 6 seconds the difference between the number of rotations of R and L gear is 2 units.
Required net difference should be 6 rotations => 3 (6 seconds later) ==> 18 seconds.
Answer: E
Gear R -- 40 rotations per 60 seconds -- 3 rotations per 6 seconds.
First 6 seconds -- Gear L makes 1 rotation. -- Gear R makes 4 rotations -- Net difference --2 rotations
Hence every 6 seconds the difference between the number of rotations of R and L gear is 2 units.
Required net difference should be 6 rotations => 3 (6 seconds later) ==> 18 seconds.
Answer: E