Thermodynamics - Weighing an aquarium

[jai6638]

Hey.. had a problem which am tryin to solve...

During an ecology experiment, an aquarium half filled with water is placed on a scale. The scale reads 195N.

a) a rock weighing 8N is added to the aquarium. If the rock sinks to the bottom of the aquarium, what will the scale read?

b) The rock is removed from the aquarium and the amount of water is adjusted until the scale again reads 195N. a fish weighing 2N is added to the aquarium. What is the scale reading with the fish in the aquarium?

would i use the equation for finding the buoyant force which = pVg coz i think its asking for the pressure the rock experiences in water which imo is buoyant force..

However, we don't have V sowhat equatoin would i use?

thanks much...

 

[vincentchan]

you don't need the bouyant force or any formulas... use your intuition...where did the rock(fish) exert a force to? and ultimately, where does the force go transfer to...

Edit: is this really a thermodynamics question?

 

[HallsofIvy]

If you have anything that weighs 195 N on a scale and then add something that weighs 8 N to the scale, the scale will read 195+ 8= 203 N, of course.

The fact that the fish is swimming in the water is irrelevant- with 195 N from the aquarium and 2 N from the fish, the total force on the scale is 197 N.

 

[jai6638]

this is embarassing! that was really easy ...

Thanks for ur help guys.. Appreciate it!