Subtopic: Type, selection, maintenance and repair of tractors and power tillers
Question Statement:
Which of the following statements regarding adding ballast to farm tractor drive tires is/are CORRECT?
Options:
(A) Liquid ballasting typically involves filling inner tubes up to $75\%$ full (valve level at the top) with water or a calcium chloride solution
(B) Calcium chloride ($CaCl_2$) is dissolved in water to act as an antifreeze and to increase the density of the ballasting liquid by up to $25\%$
(C) Adding excessive ballast on hard dry roads increases rolling resistance and tyre wear unnecessarily
(D) Tractor ballast should always be adjusted to achieve strictly $0\%$ wheel slip under maximum drawbar pull
Answer Key:
A, B, C
Step-by-Step Solution & Explanation
- **A is correct:** $75\%$ liquid fill leaves an air cushion for pneumatic shock absorption.
- **B is correct:** $CaCl_2$ prevents freezing down to $-30^\circ\text{C}$ and raises solution density to $\approx 1.25\text{ kg/L}$.
- **C is correct:** Unneeded weight wastes fuel in overcoming rolling resistance.
- **D is incorrect:** Zero slip is highly undesirable: maximum tractive efficiency occurs at $10\text{--}15\%$ slip; zero slip means severe over-ballasting and massive rolling resistance losses.