A toy matchbox car is given a push to give it an initial speed of 4 m/s at the bottom of a loop-the-loop track (so it will move on the inside of the circular track). What is the largest radius the circular loop can have if the toy car is to remain in contact with the track at the highest point? (Note: The car does not move at a constant speed while it is inside of the track as it doesn't have an engine and gravity is acting on it so its KE and PE will continually change). Ignore friction.