4. (a) A product of a number and a unit, such as 35.2m, is not called a number. What is it called? (b) What are the fundamental dimensions, fundamental SI units, and what are the dimensions and units of 9.8 m ? (c) In a sentence, convert i. 2.4in into units of feet. ii. 4m into units of km min 5. A big train is rolling downhill on a track, and a small train is rolling uphill on a collision course with the big train. Relative to the track, the big train is moving at 2, and the small train is moving at 3. Construct two reference frames, one with the big train at the origin, one with the small train at the origin. Note that after some time passes, the two trains collide