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What is the force?

A spaceman of mass 80 kg is sitting in a spacecraft near the surface of the Earth. The spacecraft is accelerating upward at five times the acceleration due to gravity. What is the force of the spaceman on the spacecraft?
 
Answer: 4800 N

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Hi Sun;
This is what is confusing me.
The spacecraft is accelerating at five times the acceleration due to gravity, 49.05 m/s2.  Isn't that slow for a spacecraft?
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2 Answers

By Newton's 3rd law, the force of the spaceman on the spacecraft is equal and opposite to the force of the spacecraft on the spaceman, which is the normal force, Fn. From Newton's 2nd law,
F = Fn - mg = ma =m (5g)
Fn = 6mg = 6*80kg*9.8m/s² ≈ 4800 N.