The radius of the wheel of a truck is 70 cm and the speed of the truck is 66 km/h, then the r.p.m. (revolution per minutes) of the wheel is
Solution
Correct Answer: Option B
We know that 66 km/hr = (66 × 100000 km)/(60 min) = 110000 cm/min
The radius of the wheel of a truck is 70 cm.
⇒ In one revolution the wheel covers a distance = circumference of the wheel = 2 × π × 70 cm.
[The circumference of a circle = 2 × π × r units where radius of circle = r unit.]
Assume that to cover 110000 centimeter n revolutions are needed per minute
\(\Rightarrow n = \;\frac{{110000}}{{2{\rm{\;}} \times {\rm{\;\pi \;}} \times {\rm{\;}}70}} = 250\)
The r.p.m. (revolution per minutes) of the wheel is 250
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