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Stonehenge

Explain why, when moving heavy objects on rollers, the object moves twice as fast as the rollers. Try a similar experiment yourself.

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Maximum Flow

Given the graph of a supply network and the maximum capacity for flow in each section find the maximum flow across the network.

Mach Attack

Stage: 5 Challenge Level: Challenge Level:1
To see the shape of the wave fronts you might want to draw $5$ wave fronts emitted by the aeroplane at times $t=0, 1, 2, 3, 4, 5$. The orgin of each wave front will depend on the position of the aeroplane when it is created; once created each will be a circle whose radius grows at the speed of sound.