Calculate Metal Density Using Tension in Water - Step by Step Guide

[Student_93]

Findind density !


A piece of metal of unknown volume is immersed in water by means of a thread. Before lowering the piece in water , the tension in the thread is 10 N .
The tension in the thread in when the piece is immersed in water is 8 N.
Find the Density of the metal?




My Attempt :

10N-8N=2N . .
Now , How to calculate volume using Newton? :/

Solve it before i come up with a zero in my exam

 

[Doc Al]

10N-8N=2N . .

OK, that's the buoyant force on the object. What does Archimedes' principle tell you?

 

[Student_93]

it tells me . .
when an object is immersed in a liquid ,the liquid applies a buoyant force which is equal to the weight of water displaced by the object.

 

[Doc Al]

it tells me . .
when an object is immersed in a liquid ,the liquid applies a buoyant force which is equal to the weight of water displaced by the object.

Right! Use that fact to figure out the volume. (What's the density of water?)

 

[Student_93]

1 gcm^3
but i still didn't get it how can i find density when i don't have the values of volume and mass?

 

[Doc Al]

but i still didn't get it how can i find density when i don't have the values of volume and mass?

(1) Use the weight of the object to find its mass.
(2) Use the buoyant force and the density of water to find its volume.

 

[Chronos]

The volume of water displaced is the volume of the suspended mass. The difference between immersed and unimmersed tension tells you the mass of the water displaced.

 

[Student_93]

why don't u solve it and give me answer? :P

 

[Student_93]

i have got it . . .
its mass is 0.2 kg
and F=p*g*v
And v=F/p*g
v=2/1000*10
v=0.0002 m^3

m=w/g
m=10/10
m=1 kg

density = Mass/Volume
=1/0.0002
density=5000 kgm^-3

 

[Doc Al]

Good!

 

[Chronos]

Physics is easy, except for the hard part.