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Concepts Of Physics MCQ Edition [Volume 1]
Exam
Concepts Of Physics MCQ Edition [Volume 1]
Subject
Physics
Chapter
Circular Motion

Concepts Of Physics MCQ Edition [Volume 1] · Physics · Circular Motion

A ceiling fan operates at 1500 rpm at full speed and has a diameter...

A ceiling fan operates at 15001500 rpm at full speed and has a diameter of 120 cm120 \text{ cm} (for the circle traced by the outer edges of its three blades). Consider a particle of mass 1 g1 \text{ g} that is stuck to the outer end of a blade. When the fan is running at full speed, what is the magnitude of the force experienced by the particle, and what is the magnitude of the force exerted by the particle on the blade along its surface?

Options

  1. A0.38 N0.38 \text{ N} and 0.38 N0.38 \text{ N}
  2. B14.8 N14.8 \text{ N} and 14.8 N14.8 \text{ N}
  3. C29.6 N29.6 \text{ N} and 29.6 N29.6 \text{ N}
  4. D14.8 N14.8 \text{ N} and 0 N0 \text{ N}

Correct answer

B. 14.8 N14.8 \text{ N} and 14.8 N14.8 \text{ N}

Step-by-step solution

The angular velocity of the fan is given by:

ω=2πN60=2π×150060=50π rad/s\omega = \dfrac{2\pi N}{60} = \dfrac{2\pi \times 1500}{60} = 50\pi \text{ rad/s}

The radius of the circular path is r=1202=60 cm=0.6 mr = \dfrac{120}{2} = 60 \text{ cm} = 0.6 \text{ m}.

The mass of the particle is m=1 g=10−3 kgm = 1 \text{ g} = 10^{-3} \text{ kg}.

The force experienced by the particle is the centripetal force required to keep it in circular motion, which is provided by the blade:

F=mω2r=10−3×(50π)2×0.6F = m\omega^2 r = 10^{-3} \times (50\pi)^2 \times 0.6

F=10−3×2500π2×0.6=1.5π2 NF = 10^{-3} \times 2500\pi^2 \times 0.6 = 1.5\pi^2 \text{ N}

Using π2≈9.87\pi^2 \approx 9.87, we get:

F≈1.5×9.87=14.8 NF \approx 1.5 \times 9.87 = 14.8 \text{ N}

By Newton's third law of motion, the particle exerts an equal and opposite force on the blade. Since the centripetal force acts radially inwards along the surface of the blade, the reaction force exerted by the particle acts radially outwards along the surface of the blade.

Thus, the magnitude of the force exerted by the particle on the blade is also 14.8 N14.8 \text{ N}.
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