A brick weighs 21 N. Measured underwater, it weighs 12 N...?

Question

A brick weighs 21 N. Measured underwater, it weighs 12 N. What is the size of the buoyant force exerted by the water on the brick?

a.33 N

b.21 N

c.12 N

d.9 N

The strength of the buoyant force acting on an object in a fluid depends on the object’s

a.mass.

b.surface area.

c.volume.

d.weight.

Answer 1

1)   d

2)  The governing rule of buoyancy is ...if the object displaces it's own weight it will float, if not it sinks.

So, therefore all four apply, and you might as well add density.

Answer 2

d  (21 -12)

c (weight of the fluid displaced by the object)

http://theoryx5.uwinnipeg.ca/physics/flu...

I don't like the way the second question is phrased it is too tricky - the boyancy force  is proportional to the volume of the fliud displaced which depends on the density of the object  - but that is not a choice-

good luck

Answer 3

9 N

volume

Answer 4

Weight in air - Buoyant Force = Weight in Water

21 N - BF = 12

BF = 9 N (Answer is d)

Answer to second question is c.) volume