40. What is the change in gravitational potential energy of a 65.5 kg astronaut lifted from Earth's surface into a circular orbit of altitude 4.50 10! km? [6 marks] 41. Two identical point sources are 4.5 cm apart, in phase and vibrating at a frequency of 10 Hz. They produce an interference pattern. At the point of the first nodal line 4.5 cm from one source and 5.0 cm from the other. a) Determine the wavelength. [2 marks] b) Determine the speed of the waves. [2 marks]