• I may be being stupid, but it seems like the whole of the first sentence is irrelevant. If the diameter is 500mm (0.5m) this makes the circumference (pi x d) roughly 1.5708. 80km (80 000m) divided by this is 50929.58(2dp). So the rotation speed is 50929.58 rotations per hour or 848.826rpm(3dp). I hope this helps and I'm not missing something obvious.
  • Hi mate, Just recognised the question from my HNC I am doing. If you fancy getting in touch I have completed 3 units so far so we could maybe help each other out. contact me at

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