A sample of a material has 20000 radioactive particles in it today. Your uncle measured 40000 radioactive particles in it 20 years ago. How many radioactive particles will the sample have 20 years from today?

Why does the equilibrium position of the spring change when a mass is added to the spring? will the mass oscillate around the new equilibrium position of the spring or the previous position without a mass attached to the spring? if the equilibrium position of the spring changes by 20 cm (assuming no initial mass) when a mass is added to the spring with constant 4.9 kg/s^2, what is the mass of the object attached to the spring?