You fly a propeller-driven model airplane on a 5.0m string in a horizontal circle. The 0.50kg airplane flies level and at a constant speed, making 1 revolution every 4s How hard must you pull on the string to keep the plane flying in a circle

Ahe-xe mixture containing a 0.75 mole fraction of helium is used for cooling electronics in an avionics application. at a temperature of 300 k and atmospheric pressure, calculate the mass fraction of helium and the mass density, molar concentration and molecular weight of the mixture. if the cooling capacity is 10 l, what is the mass of the coolant?