Physics_ heating and cooling?

Question

One way of keeping warm on a cold nite, in the days before electric blankets, was to take a hot water bottle to bed.
A) If a hot water bottle contains 1.00kg of water and when in the bed has a temperature of 90 degrees celsious, how much internal energy will it lose as it cools to 25 degrees celsious??

Answer 1

Let cp be the specific heat of water. The energy lost is

E = cp*M*∆T. For water, cp = 4.18 joule/kg*ºK

∆T in C is the same as ∆T in K; it is the temperature change.
M is the mass of the water.

Just plug in the numbers.