Circular Motion (Edexcel International A Level (IAL) Physics): Exam Questions

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.

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.

Derive the equation for centripetal acceleration  $a=\frac{v^2}{r}$ by considering the velocity of the poi ball at these two positions.

Your answer should include a vector diagram.

The poi ball completes 1.3 revolutions per second.

Calculate the acceleration of the poi ball.

radius of circular motion = 0.58 m

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

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.

A washing machine drum rotates about a horizontal axis. As the drum rotates at high speed, items of clothing move in a vertical circle resting against the inside surface of the drum.

The dot in the diagrams represents an item of clothing as it rotates with the drum.

Add labelled arrows to each diagram to show the forces acting on the item of clothing at each position.

The drum rotates at a constant speed.

Explain how the forces on the item of clothing vary between the bottom and the top of the drum.

The drum has an internal radius of $0.25\text{ m}$.

Calculate the minimum speed at which the clothing remains in contact with the drum at the top of the rotation.