Question

The wheels of a car are of diameter 80 cm each. How many complete revolutions does each wheel make in 10

minutes when the car is traveling at a speed of 66 km per hour?

Answer 1

circumference of wheel = 251.2 cm =2.51 m
speed car = 66km/h = 1100m/min

therefore, number of revolution in 10 min = 10×1100= 11000 revolutions.

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Answer 2

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The radius of car’s wheel = 80/2 = 40 cm (as D = 80 cm)

So, the circumference of wheels = 2πr = 80 π cm

Now, in one revolution, the distance covered = circumference of the wheel = 80 π cm

It is given that the distance covered by the car in 1 hr = 66km

Converting km into cm we get,

Distance covered by the car in 1hr = (66×105) cm

In 10 minutes, the distance covered will be = (66×105×10)/60 = 1100000 cm/s

∴ Distance covered by car = 11×105 cm

Now, the no. of revolutions of the wheels = (Distance covered by the car/Circumference of the wheels)

=( 11×105)/80 π = 4375.