Ex

  Physics (NTSE/Olympiad)  

2. Force & Laws Of Motion

Buoyancy

When a body is immersed in a liquid, the liquid exerts an upward force on the body called as the 'upthrust' or 'buoyant force.'
Factors affecting upthrust :
Larger the volume of the body submerged in the liquid, greater is the upthrust.
Larger the density of the liquid, greater is the upthrust.
Archimedes principle :
'Archimedes' principle states that when a body is immersed in liquid partially or completely, it experiences an upthrust equal to the weight of the liquid displaced."
or
The loss in weight of the block, i.e. buoyant force acting on the block is equal to the weight of the liquid displaced.
i.e. F = Vdg
where V = volume of the body
d = density of the liquid
g = acceleration due to gravity

Example : 16
A body weighs 300 gmf in air and 260 gmf when completely immersed in water. Calculate the following :
(i) loss in weight of the body
(ii) upthrust on the body.
Solution. Given : Weight of body in air = 300 gmf
Weight of the body in water = 260 gmf
∴ Loss in weight of the body = 300 – 260 = 40 gmf
∴ Upthrust of the body = Loss in weight = 40 gmf

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