$2 \ kg$ of ice at $-20^{\circ} C$ is mixed with $5 \ kg$ of water at $20^{\circ} C$. What is the final amount of water in the mixture (in $kg$)? (Given: specific heat of ice $= 0.5 \ cal/g^{\circ} C$,specific heat of water $= 1 \ cal/g^{\circ} C$,latent heat of fusion of ice $= 80 \ cal/g$)

$A$ steel ball of mass $200 \,g$ falls freely from a height of $20 \,m$ and bounces to a height of $10.8 \,m$ from the ground. If the energy lost in this process is absorbed by the ball, the rise in its temperature is ($g = 10 \,ms^{-2}$, specific heat capacity of steel is $460 \,Jkg^{-1} K^{-1}$). (in $^{\circ} C$)

One $kg$ of water, at $20, ^oC$, is heated in an electric kettle whose heating element has a mean (temperature averaged) resistance of $20, \Omega$. The rms voltage in the mains is $200, V$. Ignoring heat loss from the kettle, the time taken for water to evaporate fully is close to.......... $min$. [Specific heat of water $= 4200, J/kg, ^oC$, Latent heat of water $= 2260, kJ/kg$]

If in the winter season the surface temperature of a lake is $1^{\circ} C$,the temperature at the bottom of the lake will be ............

$A$ waterfall is $84 \ m$ high. If half of the potential energy of the falling water gets converted to heat,the rise in temperature of the water will be: (in $^\circ C$)

Out of the following,in which vessel will the temperature of the solution be higher after the salt is completely dissolved?