A classical mechanics problem by Alex Thang

Classical Mechanics Level 1

A train covers 60 miles between 2 p.m. and 4 p.m. How fast was it going at 3 p.m.?


The answer is 30.

Alex Thang by Alex Thang , 22, USA

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2 solutions

Sophie Crane
Sep 6, 2014

We know only that the average speed is 30mph. Within the wording of the problem, it was entirely possible for the speed of the train to vary between 2 p.m. and 4 p.m, so the instantaneous speed at 3 p.m. could have been anything at all.

3 Helpful 0 Interesting 0 Brilliant 0 Confused

Agreed with Sophie. The problem lacks data points required to obtain 30 as the answer. Two statements that could lead to the answer being 30 miles an hour could be: - The train travels at uniform velocity throughout the two hours - The train starts from rest at 2 pm and travels with uniform acceleration throughout the two hours

Aseem Raj Baranwal - 3 years, 6 months ago
Danny Pearson
Aug 4, 2014

Distance / Time = Speed

60 miles / 2 hours = 30mph

0 Helpful 0 Interesting 0 Brilliant 0 Confused

at least tell the unit. I gave answer as 48kmph ( 30*1.6 )

Ameya Ballal - 6 years, 9 months ago

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