Uniform Circular Motion - NEET Physics Questions
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Uniform Circular Motion

Practice Questions:
Question 21: easy

Assertion (A): In uniform circular motion of a body, its linear speed remains constant.

Reason (R): In uniform circular motion total acceleration of the body has no radial component.

 

1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (3) (A) is true but (R) is false
4. (4) Both (A) and (R) are false
View Answer

By definition, uniform circular motion means constant linear speed. So (A) is true. In UCM, the only acceleration is centripetal, which is entirely radial and directed towards the center. So (R) is false.

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Question 22: easy

Assertion (A): In uniform circular motion of a particle, sum of power delivered to it by all the forces acting on the particle is zero.

Reason (R): In uniform circular motion dot product of two perpendicular vectors, force and velocity is always zero.

 

1. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (3) (A) is true but (R) is false
4. (4) Both (A) and (R) are false
View Answer

In UCM, net force is perpendicular to velocity, so power \(P = \vec{F} \cdot \vec{v} = Fv \cos{90^{\circ}}\) is zero. Thus, (A) is true. Reason (R) correctly states that the dot product of perpendicular vectors is zero, which explains (A).

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Question 23: easy

Assertion (A): A coin is placed on the gramophone. When the motor starts, the coin moves along the gramophone. As the speed goes on increasing, the coin flies off after some time.

Reason (R): The gravitational force of gramophone provides the necessary centripetal force to the coin.

1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer

Assertion (A) is true: As the angular speed \( \omega \) of the gramophone increases, the required centripetal force \( m \omega^2 r \) for the coin increases. When this force exceeds the maximum static friction (\( \mu_s mg \)), the coin slips off.

Reason (R) is false: The centripetal force is provided by the frictional force between the coin and the gramophone, not by the gravitational force. Gravitational force provides the normal force.

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Question 24: easy

Assertion (A): Two identical trains move in opposite sense in equatorial plane with equal speed relative to earth’s surface. They have equal magnitude of normal reaction.

Reason (R): The trains require same centripetal force although they have different speeds.

1. Both (A) & (R) are true and the (R) is the correct explanation of the (A)
2. Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
3. (A) is true but (R) is false
4. Both (A) and (R) are false
View Answer

The absolute speed of the trains relative to Earth's center is \( v_{\text{abs}} = R_E \omega_E pm v_{\text{surface}} \). Since their absolute speeds are different, the centripetal force required \( F_c = m v_{\text{abs}}^2 / R_E \) will be different. The normal reaction is \( N = mg - F_c \), so it will also be different. Therefore, both Assertion (A) and Reason (R) are false.

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