In a demonstration, an object is suspended from a spring scale which reads 8N wh
ID: 1437512 • Letter: I
Question
In a demonstration, an object is suspended from a spring scale which reads 8N when the object is in air. The object is then lowered into a beaker of water, and when the object is fully submerged in the water, the scale reads 6N. a) Find the density of the object. b) During the entire demonstration, the beaker is standing on a kitchen scale which reads 20N before the object is lowered into the water. What does this scale read when the object is fully submerged? c) Compare the sum of the two scale readings before and after the object is submerged.
Explanation / Answer
spring scale reading when the object is in air, Fg=8N
spring scale reading when the object is in water, Fw=6N
a)
buoyant force, Fb=Fg-Fw
Fb=8-6
Fb=2N
but,
FB=rho_water*V*g
2=1000*V*9.8
====> volume of the object, V=2.04*10^-4 m^3
and
density of the object is,
rho_object=m/v
rho_object=(Fg/g)*v
rho_object=(Fg/(g*v)
rho_object=(8/(9.8*2.04*10^-4)
===> rho_object=4001.6 kg/m^3
b)
kitchen scale reading, Fk=20 N
thr scale reads the net force, Fnet=FK+Fw
Fnet=20+6
Fnet=26 N
c)
before submerged,
spring scale reading , Fs=8N
kitchen scale reading, Fk=20 N
sum of the two scale reading, F=28 N
===>
after submerged,
spring scale reading , Fs=6N
kitchen scale reading, Fk=26 N
sum of the two scale reading, F'=32 N
==>
F/F'=28/32
F/F'=0.875 or F'/F=1.143