Explanation:
The runner runs for a total time of
\Delta t=10.0 min= 600 sΔt=10.0min=600s
The energy converted by the runner during this time is equal to the power of the runner times the total time:
E=P \Delta t=400 W \cdot 600 s =2.4 \cdot 10^5 JE=PΔt=400W⋅600s=2.4⋅10
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