Question 5
Driving a vehicle whose tyre treads have worn away is dangerous on rainy days. Why?
The right answer is the one marked above.
Worn treads cannot let the water escape, so friction drops and the vehicle skids. A layer of water between tyre and road reduces the friction between the two surfaces; the treads are cut so the water underneath has somewhere to go.
"Smaller contact area" is the trap. Area does not affect friction — it is the water layer, not the missing rubber, that does the damage.