(20 1 1? Xiaoming and his father go fishing in a fish pond. Dad told Xiaoming: When you catch a big fish, don't pull it out of the water immediately, but hold the fishing rod.

(1) dad's pressure on the ground F=mg=60kg× 10N/kg=600N,

The contact area with the ground is s =120×10-4m2× 2 = 240×10-4m2.

Ground pressure P=FS=600N240× 10? 4m2=2.5× 104Pa。

A: The ground pressure is 2.5× 104 Pa.

(2) If the fish is free floating, then F floating =G fish =4kg× 10N/kg=40N,

According to Archimedes principle: F float = ρ gV drainage.

It is obtained that: V fish =V row =F floating ρ water G = 40N/kloc-0 /×103kg/m3×10n/kg = 4×10-3m3.

A: The volume of fish is 4× 10-3m3.

(3) According to the lever balance condition F 1l 1=F2l2,

F2 = f 1l 1l 2 = 200n×0.4m 4 = 20N。

Answer: At this time, the pulling force F2 of the fishing line on the fishing rod is 20N. ..