A wheel of radius 1.4 m of a car makes 70 revolutions in 1 min. What is the speed of the car (in km/h)?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 36.96
In one revolution the wheel rolls the car forward by one circumference, so the distance in a minute is the circumference times the number of revolutions in a minute.
Circumference \(\displaystyle =2\pi r=2\times\frac{22}{7}\times1.4=8.8\) m
Distance in 1 min \(=8.8\times70=616\) m
Distance in 1 h \(=616\times60=36960\) m \(=36.96\) km
The car covers 36.96 km in an hour, so its speed is 36.96 km/h