Because ice can absorb more heat from the soft drink to change its state from ice to water (latent heat), than water only.
If you use the equation for heat released/absorbed,
Let T2 = final temperature of ice (assume it's above 0°C, so it became water at some temp > 0°C)
Let T1 = initial temperature of ice (which is 0°C
Q(absorbed by ice) = latent heat + sensible heat
Q(absorbed by ice) = m*Lf + m*c*(T2 - 0)
while if water only,
Q(absorbed by water) = m*c*(T2 - 0)
Q absorbed by ice is also the Q released by soft drink.
Hope this helps :)
Why is an ice cube at 0°C more effective in cooling soft drink than the same mass of water at0°C?
2 answers
Because ice absorbs more heat than water