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Hi there! You're correct. Using initial velocity as 6 m/s and final as -6 m/s is perfectly fine.

Hi there! You're right we need 1 sig fig giving us 400,000.

The question covers approximation, but fails to account for sig figs.

Hi there! Nice question. The knees bend making the feet rise 20 cm - the jump is 20 cm above the ground.

Parts of the body not affected by bending rise about by 16cm - knees up means that trunk and head rise 16cm.