Moments and equilibriumEdexcel International A Level Physics: Subtopic test

1. 1
   A mechanic uses a spanner with a handle 0.25 m long to tighten a nut. The force is applied at the end of the handle, and the axis of rotation is the centre of the nut.

   (a)

   The mechanic applies a force of 40 N at right angles to the handle at its end. What is the moment of the force about the centre of the nut?

   [1 mark]

   • A160 N m
   • B10 N m
   • C0.0063 N m
   • D40.25 N m

   (b)

   She now pulls with the same 40 N force, but the force makes an angle of 60° with the handle. What is the moment of the force about the centre of the nut?

   [1 mark]

   • A8.7 N m
   • B5.0 N m
   • C10 N m
   • D11.5 N m

   (c)

   Explain why a longer spanner makes it easier to turn the nut.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A uniform plank of length 4.0 m and weight 200 N rests horizontally on two supports, A at its left end and B at its right end. A child of weight 600 N stands on the plank 1.0 m from A.

   (a)

   What is the total upward force exerted on the plank by the two supports?

   [1 mark]

   • A200 N
   • B600 N
   • C800 N
   • D1000 N

   (b)

   What is the force exerted by support B on the plank?

   [1 mark]

   • A550 N
   • B400 N
   • C150 N
   • D250 N

   (c)

   State what is meant by the centre of gravity of an object, and explain why the weight of the plank can be taken to act at a point 2.0 m from A.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A uniform metre rule of weight 1.0 N is pivoted on a knife edge at the 30.0 cm mark. A 2.0 N weight is hung from the 5.0 cm mark and a weight W is hung from the 90.0 cm mark. The rule balances horizontally.

   (a)

   Calculate the weight W.

   [3 marks]

   (b)

   Calculate the upward force exerted by the knife edge on the rule. The knife edge is then moved to the 50.0 cm mark with the three weights unchanged. Explain whether the rule remains balanced.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A uniform horizontal beam of length 2.0 m and weight 120 N is hinged to a vertical wall at one end. A cable joins the free end of the beam to a point on the wall above the hinge, making an angle of 30° with the beam. A load of 200 N hangs from the free end of the beam, and the system is in equilibrium.

   (a)

   Explain how the principle of moments is used to find the tension T in the cable, and calculate T.

   [6 marks]

   (b)

   The 200 N load is moved to the middle of the beam, 1.0 m from the hinge. A student claims that, because the load is moved half as far from the hinge, the tension in the cable is halved. Evaluate the student's claim.

   [6 marks]

   Total for question 4: 12 marks

End of questions