4. A group of students arrange two level tracks side-by-side so they can have a race between two carts with fans mounted on them. They start with the two fan units having the same strength (same number of batteries). Cart #2 has extra blocks on it so its mass is greater than the mass of cart #1. #2 The students next want to adjust the strength of fan unit #1 (by changing the number and size of batteries) so the two carts will tie in a race (that is, when turned on and released they will each speed up at the same rate). Should the strength of fan unit #1 be made greater than, equal to, or less than the strength of fan unit #2? Justify your