1. While running, a person dissipates about 0.502J of mechanical energy per step per kilogram of body mass. If a 55.7kg runner dissipates a power of 69.9W during a race, how fast is the person running? Assume a running step is 1.50m in length.
2. When a certain spring is stretched, the restoring force satisfies the equation F=-kx+βx^3. If k=10.4N/m and β=101N/m^3, calculate the work done by this force when the spring is stretched 0.111m