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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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Bunuel
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A wheel of a car of radius 21 cms is rotating at 600 RPM. What is the [#permalink] New post   14 Mar 2016, 08:50
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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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B
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Re: A wheel of a car of radius 21 cms is rotating at 600 RPM. What is the [#permalink] New post   14 Mar 2016, 12:03
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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] New post   28 Oct 2018, 13:38
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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 [#permalink] New post   23 Jan 2020, 11:41
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Bunuel wrote:
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


Since the radius of the wheel is 21 cm, the circumference of the tire is 21 x 2π = 42π cm. Since the wheel is rotating at 600 rotations per minute, the car is traveling at 42π x 600 cm per minute. Since there are 60 minutes in an hour, the car is traveling at 42π x 600 x 60 = 42π x 36,000 cm per hour. Since 1 km = 1000 m and 1 m = 100 cm, 1 km = 1000 x 100 = 100,000 cm, and therefore, the car is traveling at 42π x 36,000 / 100,000 = 42π x 36 / 100 ≈ 47.5 km/hr.

(Note: If we use 22/7 for π, we will have 42 x 22/7 x 36 / 100 = 6 x 22 x 36 / 100 = 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. [#permalink] New post   13 Apr 2023, 06:09
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Re: A wheel of a car of radius 21 cms is rotating at 600 RPM. [#permalink]
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