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Ask high school physics questions, consult experts and expect an analysis process.

1) The first 3s fall to h=gt*2/2=45m.

Average gravity power P=mgh/t=5* 10*45/3=750W.

(2) The formula of average power is P=Fv and F=mg=50N. The speed at the end of the second second is 20m/s, the speed at the end of the third is 30m/s, the average speed in the third second is (20+30)/2 = 25m/s, and the average power P=50*25= 1250W.

(3) The speed v3 at the end of three seconds = gt = 30m/s.

Instantaneous power at the end of the third second p' = mgv = 1500 w