Given:
Mass of copper, mc=50 g=0.05 kg
Temperature change of copper coin, ΔTc=10∘C
Specific heat of copper, Sc=420 J kg−1 K−1
Mass of water, mw=10 g=0.01 kg
Specific heat of water, Sw=4186 J kg−1 K−1.
Let the temperature change of water be ΔTw
Since, heat given to the copper is equal to the heat gained by the water,
mcScΔT=mwSwΔTw
0.05×420×10=0.01×4186×ΔTw
ΔTw=5∘C