Moments and turning effectsIB MYP Physics: Subtopic test

1. 1
   A mechanic in São Paulo uses a spanner 0.25 m long to loosen a wheel nut. She pushes at right angles to the end of the spanner with a force of 80 N, but the nut does not turn.

   (a)

   What is the unit of the moment of a force?

   [1 mark]

   • AN/m
   • BN m
   • CN/m²
   • Dkg m/s

   (b)

   What is the moment of the force she applies about the nut?

   [1 mark]

   • A320 N m
   • B80.25 N m
   • C0.0031 N m
   • D20 N m

   (c)

   She slides a long pipe over the spanner so that she can push 0.50 m from the nut with the same force. Explain why this helps her to turn the nut.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Two children sit on a see-saw that has its pivot at the centre. Child P weighs 300 N and sits 2.0 m from the pivot on the left. Child Q weighs 400 N and sits on the right. The see-saw is balanced horizontally.

   (a)

   Which statement is true about the balanced see-saw?

   [1 mark]

   • AThe two children must have equal weights
   • BThe two children must sit the same distance from the pivot
   • CThe total clockwise moment equals the total anticlockwise moment
   • DThere is a turning effect on one side of the pivot only

   (b)

   How far from the pivot does child Q sit?

   [1 mark]

   • A1.5 m
   • B2.0 m
   • C0.67 m
   • D1.0 m

   (c)

   Child Q now moves so that she sits 2.0 m from the pivot. Explain what happens to the see-saw.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student investigates balancing a uniform metre rule that is pivoted at its centre, so the weight of the rule itself has no turning effect. A 4.0 N load is hung 0.30 m to the left of the pivot. She hangs different weights on the right and moves each one until the rule balances. A 2.0 N weight balanced at 0.60 m from the pivot, a 3.0 N weight at 0.40 m and a 6.0 N weight at 0.20 m.

   (a)

   State the independent variable, the dependent variable and one control variable in this investigation.

   [3 marks]

   (b)

   Calculate the moments in the investigation. State whether the results support the principle of moments and suggest one improvement.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A transport authority in Hong Kong runs double-decker buses. Each bus is tested by tilting it on a platform to see how far it can lean before it tips over. Passengers standing on the upper deck raise the centre of mass of the bus. The authority is deciding whether to ban standing passengers on the upper deck.

   (a)

   Explain what is meant by the centre of mass. Explain why a low centre of mass and a wide base make a bus more stable, and why standing passengers on the upper deck make the bus less stable.

   [6 marks]

   (b)

   Discuss and evaluate the authority's decision to ban standing passengers on the upper deck.

   [6 marks]

   Total for question 4: 12 marks

End of questions