Overview
Problem 1:
A man (the system) walks inside an isolated room for 5 hours and does W=1250 JW = 1250 \, \text{J}W=1250J of work. The internal energy decreases by ΔU=−2250 J\Delta U = -2250 \, \text{J}ΔU=−2250J. Determine the heat QQQ (with sign).
Follow-up:
If the system instead gains
3000 J3000 \, \text{J}3000J of heat while performing the same work (W=1250 JW = 1250 \, \text{J}W=1250J), what is the change in internal energy?Problem 2: At constant pressure p=2.5×105 Pap = 2.5 \times 10^{5} \, \text{Pa}p=2.5×105Pa, the system does W=4500 JW = 4500 \, \text{J}W=4500J of work. Find the change in volume ΔV\Delta VΔV.
Problem 3: An isothermal compression of an ideal gas: n=4n = 4n=4 moles, initial temperature T=375 KT = 375 \, \text{K}T=375K. The gas is compressed to one-fifth of its initial volume (Vf=Vi/5V_f = V_i / 5Vf=Vi/5). How much heat is removed during the compression?
Problem 4: A car engine with efficiency η=30.0%\eta = 30.0\%η=30.0% produces W=4000 JW = 4000 \, \text{J}W=4000J of work. How much heat is rejected by the engine?
Problem 5: A Carnot (ideal) heat pump heats a house kept at TH=300 KT_H = 300 \, \text{K}TH=300K; outside temperature is TC=265 KT_C = 265 \, \text{K}TC=265K. How much work must the pump do to deliver QH=5000 JQ_H = 5000 \, \text{J}QH=5000J of heat into the house?