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Firework Rocket

Problem

A firework rocket is fired vertically upwards with a constant acceleration of 4 ms-2 until the chemical fuel expires. Its ascent is then slowed by gravity until it reaches a maximum height of 138 metres.

Assuming no air resistance and taking g=9.8 ms-2, how long does it take to reach its maximum height?

Problem ID: 161 (Mar 2004)     Difficulty: 4 Star

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