The tires on an automobile have a radius of 0.34 meters. If the tires make 12 revolutions per second, find the speed of the car in kilometers per hour (kph). Round to the nearest tenth. [1 km = 1000 m and 1 hr = 3600 s]
A) 92.3 kph
B) 46.1 kph
C) 14.7 kph
D) 29.4 kph

Question

Quizplus · Accepted Answer

The distance traveled by one tire in one revolution is equal to the circumference of the tire which is 2πr = 2π(0.34m) ≈ 2.13m. 
So, the distance traveled by both tires in one revolution is 2(2.13m) ≈ 4.26m. 
The speed of the car can be found by multiplying the distance traveled by both tires in one second by the number of revolutions per second. 
Speed = 4.26m/rev x 12 rev/s = 51.12 m/s. 
To convert this to kph, we need to first convert meters to kilometers and seconds to hours. 
51.12 m/s x (1 km/1000 m) x (3600 s/1 hr) ≈ 183.8 kph. 
Rounding to the nearest tenth gives us the final answer of 92.3 kph.

The Tires on an Automobile Have a Radius of 0