Question

If the diameter of each of a car's wheels is 0.4 meters, approximately, what was the average speed of the car for its three-hour trip in which each wheel made 100,000 revolutions?

Answer 1

Answer:

42 km/h was the average speed of the car for its three-hour trip.

Explanation:

Diameter of the car wheel = d = 0.4 m

Radius of the car wheel = r = 0.5 d = 0.5 × 0.4 m =0.2 m

Distance covered in 1 complete revolution = $2\pi r$

Distance covered in 100,000 complete revolution,D = $2\pi r\times 100,000$

$D=2\times 3.14\times 0.2 m\times 100,000=125,663.71 m$

1 m = 0.001 km

125,663.71 m = 125,663.71 × 0.001 km = 125.66371 km

Time taken to complete 100,000 revolution by a wheel = t = 3 hours

Speed of car : S

$S=\frac{125.66371 km}{3hours}=41.89 km/h\approx 42 km/h$

42 km/h was the average speed of the car for its three-hour trip.

Answer 2

Answer:

Explanation:

diameter = 0.4 m

Radius, r = 0.2 m

Time, t = 3 hour

number of revolutions, = 100,000

Distance traveled in one revolution = 2 x π x r = 2 x 3.14 x 0.2 = 1.256 m

Total distance in 100,000 revolutions,

d = 100,000 x 1.256 = 125600 m

d = 125.6 km

Average speed = distance / time

Average speed = 125.6 / 3 = 41.87 km/h