A 0.200kg piece of copper at 90∘C is dropped into a mass mw of water at 15∘C contained in an insulated vessel. If the final equilibrium temperature is 25∘C, what is mw? (Specific heats: cCu=386Jkg−1∘C−1, cw=4186Jkg−1∘C−1.)
a) 240g
b) 120g
c) 60g
d) 280g