He marks each section and dives into algebra. Working with Newton’s laws, he estimates masses and sketches pulleys in pencil. I can see a shortcut to his answer – a little less than 6.5 m/s2. He has approached the problem from first principles – a child churning through possibilities. I look again as we pass Cathays – 6.47 m/s2. He got there. When I get off at Queen Street I leave a tick on the seat beside him.
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