12. An electric train travels at a constant speed on a circular track with a radius of 0.7 m. It takes the train 5.0 s to change its heading from east to south. Calculate the train's: a) b) c) d) average speed change in velocity average acceleration instantaneous acceleration (0.22 m/s, 0.311 m/s [SW], 0.0622 m/s [SW], 0.0691m/s)