Posted by **Ellen** on Wednesday, March 24, 2010 at 4:15pm.

A hollow plastic spherical bobber of mass 0.005 kg and volume of 50 cm3 floats on the surface of a lake supporting a submersed fishhook and a bait with a combined mass of 0.01 kg and a combined volume of 2 cm3. The density of water is 0.001 kg/cm3.

If a fish grabs the bait, find the minimum downward force, Ffish, it must exert to pull the bobber completely under the surface of the water. You may assume that the apparent weight of the fish is zero, and the fishing line is completely slack.

- Physics -
**bobpursley**, Wednesday, March 24, 2010 at 4:54pm
So you want the bouyant force of the submerged bob.

Mass: .005+.01 kg

Volume: 50cm^2+2cm^2

mass of displaced water: densitywater*volume=1g/cm^3*52cm^2=52g

bouyant force= 9.8N/Kg * (.052kg)

net force=9.8(52-15)N

check my thinking.

- Physics -
**Ellen**, Thursday, March 25, 2010 at 10:25am
thank you so so so much. the answer is .3626

- Physics -
**Hamza**, Friday, July 22, 2016 at 7:22pm
The force that is

- Physics -
**Hamza**, Friday, July 22, 2016 at 7:24pm
The force that is exerted by the bobber and the hook and bait will be equal to the combined mass and the combined volume (0.015 kg and 52 cm^3)-- not sure why though.

The buoyant force if the object was completely submerged would be the density of water*V displaced*g (.001*52*9.8).

The difference between these two (0.3626) would be the force the fish would need to exert to completely submerge the bobber.

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