Which has a greater buoyant force on it, a 25.0 cm3 piece of wood floating with

piece of submerged iron

Explanation:

The buoyant force is given by:

where

is the density of the liquid (in this case, water)

is the submerged part of the object

g is the acceleration due to gravity

In this problem, the liquid used in the two examples is the same, water, so is the same; and g is the same as well. Therefore, the only difference between the two examples is .

For the piece of wood, we are told that the object is floating, so only a fraction of its total volume of 25.0 cm3 will be submerged: therefore the submerged volume will be less than 25.0 cm3. On the contrary, the problem tells us that the piece of iron is submerged, so the submerged volume in this case is 25.0 cm3. Therefore, the submerged volume for the iron is greater than for the piece of wood, so the buoyant force of the piece of iron is greater.

1)  ΔE = -800 J, 2) ΔE = 200 J, 3)  ΔE = -200 J, 4) ΔE = 800 J

Explanation:

For this exercise let's use the first law of thermodynamics

          ΔE = Q + W

Where we will apply this expression to several cases

1) output Q = 500 J and does work of W = 300 J.

The two processes involve an energy output

         ΔE = - 500 - 300

         ΔE = -800 J

Therefore, the internal energy of the gas decreases by this amount,

2) enter Q = 500J and do work of W = 300 J

         Positive heat is added and does negative work

         ΔE = 500 - 300

         ΔE = 200 J

3) they leave Q = 500 J and do (work on the gas) W = 300J

negative heat and positive work come out

          ΔE = -500 + 300

          ΔE = -200 J

4) heat enters Q = 500 J, work on gas W = 300 J

both positive

         ΔE = 500 + 300

         ΔE = 800 J