A steel wire is suspended vertically from a rigid support When loaded with a weight in air it expands by La and when the weight is immersed completely in water the extension is reduced to Lw Then relative density of the material of the weight is
A
LaLa−Lw
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B
LwLa
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C
LaLw
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D
LwLa−Lw
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Solution
The correct option is ALaLa−Lw From Young's relation,
Stress ∝ Strain
F∝x
where F is the force acting causing the wire to stretch, and x is the extension of the wire on application of the force.
Hence Wa=kLa
and Ww=kLw
The weight in water is the resultant of weight in air and the buoyant force acting upwards.