While walking along the beach John gives off 120 kj of heat andn his internal energy decreases by 260 kj. How much work is done while walking?
To find the amount of work done while walking, we can use the First Law of Thermodynamics, which states that the change in internal energy (ΔU) of a system is equal to the heat added or removed from the system (Q) plus the work done (W) on or by the system.
The equation can be expressed as: ΔU = Q + W
Given that John gives off 120 kJ of heat (Q = -120 kJ) and his internal energy decreases by 260 kJ (ΔU = -260 kJ), we can substitute these values into the equation:
-260 kJ = -120 kJ + W
To find the value of W, we need to isolate it on one side of the equation. To do this, we can add 120 kJ to both sides of the equation:
-260 kJ + 120 kJ = -120 kJ + W + 120 kJ
Simplifying the equation:
-140 kJ = W
Therefore, the amount of work done while walking is -140 kJ. The negative sign indicates that work is done on John (by an external force) rather than him doing work.