Centripetal forceEdexcel A-Level Physics: Subtopic test

1. 1
   A puck of mass 0.25 kg is attached to a light string, the other end of which is fixed to a smooth horizontal table. The puck moves in a horizontal circle of radius 0.80 m at a constant speed of 4.0 m s⁻¹.

   (a)

   Which force provides the centripetal force on the puck?

   [1 mark]

   • AThe weight of the puck
   • BThe tension in the string
   • CThe normal contact force from the table
   • DA centrifugal force acting outwards on the puck

   (b)

   Which statement about the resultant force on the puck is correct?

   [1 mark]

   • AIt is zero, because the speed is constant
   • BIt acts in the direction of the velocity
   • CIt acts away from the centre of the circle
   • DIt acts towards the centre, perpendicular to the velocity

   (c)

   Calculate the tension in the string.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A car of mass 1200 kg travels at a constant speed of 14 m s⁻¹ round a flat, circular roundabout of radius 25 m. The maximum sideways frictional force that the tyres can exert on the road surface is 8.0 kN.

   (a)

   Which force provides the centripetal force on the car?

   [1 mark]

   • AThe sideways friction between the tyres and the road
   • BThe driving force from the engine
   • CThe weight of the car
   • DThe air resistance on the car

   (b)

   The car goes round the same roundabout at twice the speed. By what factor does the resultant force needed to keep it on the circle change?

   [1 mark]

   • AIt is doubled
   • BIt is halved
   • CIt is multiplied by 4
   • DIt is unchanged

   (c)

   Deduce whether the car can travel round the roundabout at 14 m s⁻¹ without skidding.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A fairground 'rotor' ride is a vertical cylinder of radius 2.5 m that rotates about its vertical axis at a constant angular speed of 3.0 rad s⁻¹. A rider of mass 60 kg stands against the inside wall of the cylinder. Once the cylinder is rotating at full speed the floor is lowered, and the rider stays in contact with the wall without sliding down.

   (a)

   Calculate the speed of the rider and the resultant force on the rider.

   [3 marks]

   (b)

   Explain how the rider is able to stay against the wall without sliding down, and calculate the frictional force on the rider.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A car of mass 900 kg travels at a constant speed of 15 m s⁻¹ over the top of a hump-back bridge. The top of the bridge is part of a vertical circle of radius 45 m. Later the car travels at the same speed through the bottom of a dip in the road that is also part of a circle of radius 45 m.

   (a)

   Calculate the contact force exerted by the road on the car at the top of the bridge, and calculate the speed at which the car would just lose contact with the road at the top.

   [6 marks]

   (b)

   A passenger says that she feels lighter at the top of the bridge and heavier at the bottom of the dip. Evaluate her claim using calculations for the contact force on the car at each position.

   [6 marks]

   Total for question 4: 12 marks

End of questions