Circular Motion (Edexcel International A Level Physics)

Exam Questions

28 mins4 questions
1a
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2 marks

18th century clocks sometimes used a conical pendulum to measure regular periods of time.

A conical pendulum consists of a bob of mass m fixed to the end of a wire of length l as shown. The bob is set to follow a circular path in the horizontal plane. The wire makes an angle θ with the vertical.

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Add to the diagram to show the two forces acting on the bob.

1b
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7 marks

i) Derive the following equation for the angular velocity ω of the bob.

omega space equals space square root of fraction numerator g over denominator l space cos space theta end fraction end root

(4)

ii) A clock requires the period of the bob to be 5.0 s.  

l = 6.4 m

θ = 13.9°  

Deduce whether this arrangement leads to the required period.

(3)

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2a
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5 marks

A poi ball is a ball attached to a person’s hand by a cord. A child makes the poi ball undergo circular motion in a vertical plane as shown in the photograph.

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The poi ball moves clockwise in a circle of radius r, centre O, with a constant speed v.

The diagram shows two positions, A and B, of the poi ball.

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Derive the equation for centripetal acceleration  a equals v squared over r by considering the velocity of the poi ball at these two positions.

Your answer should include a vector diagram.

2b
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3 marks

The poi ball completes 1.3 revolutions per second.

Calculate the acceleration of the poi ball.

radius of circular motion = 0.58 m

Acceleration = ..............................

2c
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4 marks

The child comments that as the ball goes round the circle with a constant speed, the size of the force on his hand changes.

Discuss whether this comment is correct.

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1
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6 marks

The photograph shows a track for a toy car. The car moves down the track towards a circular loop. The loop starts at point A.

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If the release point of the car is high enough, the car moves fast enough to pass point C and complete the loop, continuing to the end of the track at point D.

If the release point is too low, the car falls off the track between point B and point C.

Deduce whether a car released from a vertical height of 25 cm above point A will complete the loop and reach point D. You should assume that friction is negligible.

vertical height of point C above point A = 22 cm

mass of toy car = 33 g

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