Weekly Brain Teaser | Consider a vertical wheel of radius 10 cm
Every week we feature a Brain Teaser or a thought-provoking question.
If you have one that you would like to share with fellow engineers, please email it to info@engineeringdaily.net.
So, here is this week’s,
Consider a vertical wheel of radius 10 cm. Now suppose a smaller wheel of radius 2 cm, is made to roll around the larger wheel in the same vertical plane while the larger wheel remains fixed.
What is the total number of rotations the smaller wheel makes when its center makes one complete rotation about the larger wheel?
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artie are you sure your “rotations” are 360 degrees?
I kept the 10 cm radius circle stationary and rotated the 2 cm radius circle about it, marking each complete revolution on the larger circle. After one trip around the large circle there were 5 equally spaced marks, not six. Good call Dave.
It appears that we can’t seem to agree on the correct answer. Can anyone provide a video, schematic excel worksheet or other type of evidence to back their answer?
Thank you all for participating.
also both wheels are on the same 2-dimensional plane
you have to remember that the large wheel is stationary and the smaller wheel is moving along the edge. thats the key to this brain teaser.
it takes 6 full rotations (360 degrees each) to make it all the way around
if both wheels were stationary, like a couple of gears, then it would be 5 rotations
5 is correct – I gave it a spin.
6 is the correct answer.
If you can not visualize it, make yourself some cardboard cut-outs and give it a spin. Empirical evidence will always trump endless babbling.
fixed