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

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New post 14 Mar 2016, 07:50
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A
B
C
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E

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Question Stats:

63% (02:10) correct 37% (02:22) wrong based on 147 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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New post 14 Mar 2016, 11:03
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
Answer B
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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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New post 28 Oct 2018, 12:38

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

Correct answer: Option B
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Re: A wheel of a car of radius 21 cms is rotating at 600 RPM. What is the &nbs [#permalink] 28 Oct 2018, 12:38
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