Assertion (A): In turning a vehicle safely with uniform speed in circular path friction is static in nature and towards centre.
Reason (R): In turning a vehicle in circular path with increasing speed friction is kinetic in nature and tangential in direction.
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
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For safe turning at uniform speed, static friction provides the necessary centripetal force towards the center. So (A) is true. If speed increases, kinetic friction might act but it's not tangential; it opposes relative motion. So (R) is false.
Assertion (A): In uniform circular motion, magnitude of acceleration is \(\frac{V^2}{R}\) and direction is always towards the centre.
Reason (R): In uniform circular motion, acceleration is constant.
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
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In UCM, centripetal acceleration is \(a = \frac{V^2}{R}\) towards the center. So (A) is true. Acceleration direction continuously changes, so it's not constant. So (R) is false.
Assertion (A): Whenever a particle moves in a circular path with uniform speed, an acceleration exists which is directed towards the centre
Reason (R): The net acceleration of a particle in circular motion is always radially inward.
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
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In UCM, there is always centripetal acceleration towards the center, even if speed is uniform, due to change in velocity direction. So (A) is true. In UCM, the only acceleration is centripetal, which is radially inward. So (R) is true and explains (A).
Assertion (A): If the speed of a body is constant, the body cannot have a path other than a circular or straight line path.
Reason (R): It is not possible for a body to have a constant speed in an accelerated motion.
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
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A body can have constant speed and follow a curvilinear path (e.g., parabolic trajectory if air resistance is ignored). So (A) is false. A body can have constant speed but changing direction, leading to acceleration (e.g., UCM). So (R) is false.
Assertion (A): In circular motion, centripetal and centrifugal forces act in opposite directions and balance each other.
Reason (R): Centripetal force is a pseudo force.
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
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Centripetal force is a real force causing circular motion. Centrifugal force is a pseudo force in a non-inertial frame. They are not interaction pairs and do not balance each other. So (A) is false. Centripetal force is a real force. So (R) is false.
Assertion (A): In non-uniform circular motion, linear speed of the body is variable.
Reason (R): In non-uniform circular motion, acceleration of the body is towards the centre.
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
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In non-uniform circular motion, linear speed is variable, so (A) is true. The net acceleration has both radial (centripetal) and tangential components, so it's not solely towards the center. Thus, (R) is false.
Assertion (A): A body is moving along a circle with a variable angular speed. Work done by centripetal force will be zero.
Reason (R): In non-uniform circular motion, net force on the body is not in the radial direction.
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
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Centripetal force is always perpendicular to displacement, so work done by it is zero. Thus, (A) is true. In non-uniform circular motion, a tangential force exists, so the net force is not purely radial. Thus, (R) is true. However, (R) does not explain (A).
Assertion (A): A body tied to an end of a string is whirled along a vertical circle by giving some velocity at the lowest position. If the velocity becomes zero before the tension in the string is zero, the body will leave the circular path at the position of its zero velocity and then fall vertically downward.
Reason (R): In vertical circular motion, tension in the string at the highest position is maximum.
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
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If velocity becomes zero before tension, the object leaves the circular path and follows a parabolic trajectory, not vertically downward. So (A) is false.
Tension is maximum at the lowest point and minimum at the highest point in vertical circular motion. So (R) is false.
Assertion (A): A body tied to an end of a string is whirled along a vertical circle with such a velocity at the lowest point that, at some position, tension in the string is zero but the speed at the position is non-zero. The body will leave the circular path at the position of zero tension.
Reason (R): In vertical circular motion, so as to cross the highest point along the circle, speed at the highest point, \( v_H geq 0 \).
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
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An object leaves a vertical circular path when tension becomes zero and speed is non-zero. So (A) is true. To complete a vertical circle, the minimum speed at the highest point is \( \sqrt{gR} \), not just \( 0 \). So (R) is false.
Assertion (A): When an automobile while going too fast around a curve overturns, its inner wheels leave the ground first.
Reason (R): The inner wheels are moving in a circle of smaller radius, the maximum permissible velocity for them is less.
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
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Assertion (A) is true: Overturning occurs when the centrifugal force moment exceeds the stabilizing moment, causing the inner wheels to lift.
Reason (R) is true: The maximum safe velocity \( v_{\text{max}} = \sqrt{mu gr} \), so a smaller radius \( r \) means a smaller \( v_{\text{max}} \). However, (R) does not explain the overturning mechanism itself. Thus, (R) is not the correct explanation of (A).