Help!! a sample of a radioctive isotope is placed near to the radion detector and a count rate of 112 counts / minute is recorded after 18 hours the count rate is 28 counts / minute determine the half-life of this isotope

Two kilograms of air within a piston–cylinder assembly executes a carnot power cycle with maximum and minimum temperatures of 800 k and 300 k, respectively. the heat transfer to the air during the isothermal expansion is 60 kj. at the end of the isothermal expansion the volume is 0.4 m3. assume the ideal gas model for the air. determine the thermal efficiency, the volume at the beginning of the isothermal expansion, in m3, and the work during the adiabatic expansion, in kj.