1.

From what height a piece of ice at zero degree fall in order that it may melt on reaching the ground, assumin8 no loss of energY on the way : (J=4 cdot 2J// cal):

Answer»

`3 cdot 4xx10^(6) cm`
`3 cdot 4 xx10^(5) cm`
`3 cdot 4 xx 10^(6) mts`
`3 cdot 4 xx10^(5) cm`

Solution :LET m be mas of ice BLOCK and h be the height above the ground.
`therefore` Work done W=mgh.
Heat produced `Q=(W)/(J) =(mgh)/(J)`
Heat REQUIRED to melt ice block Q.=mL
`therefore (mgh)/(J)=mL`
`h=(JL)/(g)=(4 cdot 2 xx80xx10^(3))/(9 cdot 8)`
`=3 cdot 4xx10^(4)m =3 cdot 4 xx10^(6) cm`
Thus, correct choice is (a).


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