A block flats in water at `4^(0)C` so that `0.984` of its height is under water. At what temperature of water will the block just sink in water? Negleact expansion of block.
`(gamma_(R ) "for water"=2.1xx10^(-4)//^(0)C)`

Explanation

Let `d_(1) -` density of water at `4^(0@)C`
`d_(2) -` density of the water at `1^(@)C`
`d_(3) -` density of block at `t^(@)C`
`d_(2) = (d_(1))/(1 + gammaDeltat), d_(1) = 1g // c.c, d_(3) = 0.984g // c.c.`
The block sink when the density of the block and water are equal `d_(2) = (d_(1))/(1 + gammat) = d_(3)`
`0.984 = (1)/(1 + 2.1 xx 10^(-4)(t - 4))`
`1 + 2.1 xx 10^(-4)(t - 4) = (1)/(0.984)`
`rArr t - 4 = (8 xx 10^(4))/(492 xx 2.1) = 77.43^(@)C`
It must be heated to `'t' = 77.43 + 4 = 81.43^(@)C`