You attach a cart with a mass of 2.6 kg to a spring and compress the cart-spring system so that the cart is located 40 cm behind the springs equilibrium point. If the cart is released and has a velocity of 2.0 m/s when it reaches the equilibrium position, what is the spring constant k?

Awelder using a tank of volume 7.50×10^-2 m^3 fills it with oxygen (with a molar mass of 32.0 g/mol ) at a gauge pressure of 3.30×10^5 pa and temperature of 37.1 ∘c. the tank has a small leak, and in time some of the oxygen leaks out. on a day when the temperature is 23.1 ∘c, the gauge pressure of the oxygen in the tank is 2.00×10^5 pa . a) find the initial mass of oxygen. b) find the mass of oxygen that has leaked out.