# Heat and the First Law of Thermodynamics

1. Jan 9, 2006

### cmilho10

Consider Joule's apparatus described in Figure 20.1. Each of the two masses is 1.50 kg, and the tank is filled with 190 g of water. What is the increase in the temperature of the water after the masses fall through a distance of 3.50 m?

For this I know that PE=W, and that 2mgh is proportional to the change in temperature, but for some reason I can't get the correct answer

2(1.5 g)(9.8 m/s2)(3.5m)=103 C, but this is not correct

2. Jan 9, 2006

### Staff: Mentor

What you calculated is the work done in Joules, not the change in temperature. But the temperature change is proportional to the work done, but proportional does not mean equal. The relationship is as follows:
$$W = c m \Delta T$$

Where c is the specific heat of water (look it up) and m is the mass of the water.

Last edited: Jan 9, 2006