Avoid overspeeding

Geometry Level 2

Find the speed of the car with wheels of one-meter​ diameter which complete 7 rotations in 1 second.

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22.7 km/h 79.2 km/h 22 km/h 7 km/h

Sandeep Bhardwaj by Sandeep Bhardwaj , 28, India

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1 solution

Zee Ell
Aug 19, 2016

The circumference of the wheel:

dπ = 1 m × π = π m

The number of rotations in 1 hour:

3600 s × 7 1/s = 25200

Distance travelled in 1 hour:

25200 × π m = 79168.1349 m = 79168.1349 km = 79.2 km (1 d. p.)

Therefore, the speed of the car is:

v = d i s t a n c e t i m e = 79.2 km 1 h = 79.2 km/h v = \frac {distance}{time} = \frac {79.2 \text { km}}{1 \text { h}} = \boxed {79.2 \text { km/h}}

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