AQA AS Physics

Topic Questions

4.2 Moments

1a3 marks

State the principle of moments.

1b2 marks

Figure 1 shows a bicycle brake lever that has been pulled with a 50 N force to apply the brake. 

Figure 1

4-2-s-q--q1b-medium-aqa-a-level-physics

Draw two arrows on Figure 1 to show the directions of the tension in the brake cable and the force applied by the cyclist on the brake lever.

1c3 marks

Calculate the moment of the force applied by the cyclist about the pivot. State an appropriate unit.

1d3 marks

Calculate the tension in the brake cable. Assume the weight of the lever is negligible.

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2a2 marks

A waiter holds a uniform tray of mass 150 g horizontally in one hand between their fingers and thumb as shown in Figure 1. 

Figure 1

4-2-s-q--q2a-medium-aqa-a-level-physics

X, Y and W are the three forces acting on the tray. 

Describe the relationships between the forces that must be satisfied if the tray is to remain horizontal and in equilibrium.

2b3 marks

Calculate the length of the tray. Explain any assumptions made. 

2c4 marks

Calculate the magnitude of the force X and Y.

2d2 marks

The waiter places a glass of water on the tray.

State and explain where the glass should be position on the tray if the force X is to have the same value as in part (c).

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3a1 mark

It is said that Archimedes used huge levers to sink Roman ships invading the city of Syracuse. A possible system is shown in the figure 1 where a rope is hooked on to the front of the ship and the lever is pulled by several men. 

Figure 1

4-2-s-q--q4a-medium-aqa-a-level-physics

Calculate the mass of the ship if its weight is 4.6 × 104 N.

3b2 marks

Calculate the moment of the ship’s weight about point P. State an appropriate unit for your answer.

3c2 marks

Calculate the minimum vertical force, T, required to start to raise the front of the ship. Assume the ship pivots about point P.

3d3 marks

Calculate the minimum force, F, that must be exerted to start to raise the front of the ship.

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4a4 marks

The torque of a couple is given by 

                  torque = F × s 

With the aid of a diagram explain what is meant by a couple. Label Fand s on your diagram. State the appropriate unit for the torque of a couple.

4b2 marks

The see-saw shown in Figure 1 consists of a uniform beam freely pivoted at the centre of the beam. Two children sit opposite each other so that the see-saw is in equilibrium.

Figure 1

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Explain why the see-saw is in equilibrium.

4c2 marks

Explain why the weight of the beam does not affect equilibrium.

4d2 marks

Figure 2 shows the see-saw with three children of weights 460 N, 310 N and 240 N sitting so that the see-saw is in equilibrium. 

Figure 2

4-2-s-q--q5d-medium-aqa-a-level-physics

Calculate the distance, d.

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