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# A wheel of a car of radius 21 cms is rotating at 600 RPM. What is the

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Math Expert
Joined: 02 Sep 2009
Posts: 58381
A wheel of a car of radius 21 cms is rotating at 600 RPM. What is the  [#permalink]

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14 Mar 2016, 08:50
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Difficulty:

55% (hard)

Question Stats:

64% (02:27) correct 36% (02:30) wrong based on 168 sessions

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A wheel of a car of radius 21 cms is rotating at 600 rotations per minute. What is the speed of the car in km/hr?

A. 79.2 km/hr
B. 47.52 km/hr
C. 39.6 km/hr
D. 7.92 km/hr
E. 3.96 km/hr

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Re: A wheel of a car of radius 21 cms is rotating at 600 RPM. What is the  [#permalink]

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14 Mar 2016, 12:03
Radius of wheel, r = 21 cm = .21 m
Circumference
= 2 * $$\pi$$* r
= 2* 22/7 * 21/ 100
= 1.32 m

Number of rotations per min = 600
Speed of car = 600* 1.32 * 10^-3 * 60
= 36 * 10^3 * 10^-3 * 1.32
= 47.52 km/ hr
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Re: A wheel of a car of radius 21 cms is rotating at 600 RPM. What is the  [#permalink]

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28 Oct 2018, 13:38

Solution

Given:
The radius of car wheel is 21 cms.
R= 21 cms= 0.21 m
Car wheel is rotating at 600 rotations per minute

To find:
The speed of the car in km/hr.

Approach and Working

We need the speed of the car in km/hr.
Therefore, we have to find how many kms, the car travels in 1 hour.
For that we have to find the distance the car wheel covers in 1 hour.
And, in 1 min, the car wheel rotates 600 times.
Therefore, in 1 hours, the car wheel makes 600*60 rotations.
Thus, we have to find the distance car wheel covers in rotation.

In 1 rotation, the car wheel covers distance equal to its own circumference.
The distance covered in 1 revolution= Circumference of wheel= 2* π* .21= 0.42 * 22/7= 1.32 m.
Distance covered in 600 rotation= 1.32*600*60= 1.32* 36*1000=47.52 *1000 mts=47.52 kms

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Re: A wheel of a car of radius 21 cms is rotating at 600 RPM. What is the   [#permalink] 28 Oct 2018, 13:38
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