Moments & LeversOxford AQA IGCSE Physics: Subtopic test

1. 1
   Two children sit on opposite sides of a playground seesaw, which is balanced on a central pivot, and try to keep the seesaw level by adjusting how far each sits from the pivot.

   (a)

   One child pushes down on their side, turning the seesaw clockwise about the pivot. Which quantity is calculated by multiplying this child's weight by their perpendicular distance from the pivot?

   [1 mark]

   • AMomentum
   • BMoment
   • CVelocity
   • DKinetic energy

   (b)

   The heavier child sits closer to the pivot than the lighter child, and the seesaw balances perfectly level. What can be said about the moments produced by each child about the pivot?

   [1 mark]

   • AThe clockwise moment is greater than the anticlockwise moment
   • BThe anticlockwise moment is greater than the clockwise moment
   • CThe clockwise moment equals the anticlockwise moment
   • DThere are no moments acting, since the seesaw is balanced

   (c)

   The heavier child has a weight of 480 N and sits 1.2 m from the pivot. Calculate the moment this child produces about the pivot, and state the equation you used, including the correct unit for moment.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A construction worker uses a long metal crowbar to lever up one edge of a heavy paving slab, placing a small block of wood close to the slab to act as a pivot, and pushing down on the far end of the bar.

   (a)

   Why does this arrangement allow the worker to lift the heavy slab using a relatively small force at the far end of the bar?

   [1 mark]

   • AThe crowbar acts as a lever, multiplying the turning effect of the worker's smaller force
   • BThe crowbar removes the effect of the slab's weight entirely
   • CThe crowbar converts the worker's force directly into heat energy
   • DThe wooden block reduces the slab's weight

   (b)

   The worker finds the slab still won't lift, so moves the wooden block pivot even closer to the slab, keeping the same push force applied at the same point on the far end of the bar. What effect does this have on the moment produced by the worker's push about the new pivot position?

   [1 mark]

   • AThe moment decreases, since the distance from the pivot to the applied force decreases
   • BThe moment becomes zero
   • CThe moment stays exactly the same
   • DThe moment increases, since the distance from the pivot to the applied force increases

   (c)

   The worker applies a downward force of 150 N at a point 1.6 m from the new pivot position. Calculate the moment produced by the worker, and explain why this arrangement allows the worker to lift a slab weighing far more than 150 N.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A warehouse manager tests a horizontal storage shelf that is supported at one end by a wall bracket and balanced by a hanging counterweight on a cable at the other end, with the shelf's central support acting as the pivot.

   (a)

   A box of mass 40 kg is placed on the shelf 0.5 m from the pivot on one side. State the principle of moments, and calculate the moment produced by the box's weight about the pivot (take gravitational field strength as 10 N/kg).

   [3 marks]

   (b)

   For the shelf to remain balanced and level, the counterweight must produce an equal and opposite moment to the box. If the counterweight hangs 0.8 m from the pivot on the opposite side, calculate the force the counterweight must exert to keep the shelf balanced, and explain what would happen to the shelf if the counterweight's force were too small.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Historians studying medieval siege engines examine a trebuchet, a large lever-based machine used to launch stones at castle walls, consisting of a long wooden beam pivoting on a raised frame, with a heavy counterweight near the pivot on one side and a sling holding a stone far from the pivot on the other side.

   (a)

   Explain, using the ideas of moments and levers, how this design allows a relatively small counterweight drop to launch a stone at high speed, and explain the roles of force and distance from the pivot on each side of the beam.

   [6 marks]

   (b)

   The historians also note that trebuchets were sometimes built with an adjustable pivot point, allowing operators to move the pivot closer to or further from the counterweight side of the beam. Explain, using the principle of moments, why moving the pivot closer to the counterweight would change the range or speed of the launched stone, and explain any practical limit to how close the pivot could be moved to the counterweight side.

   [6 marks]

   Total for question 4: 12 marks

End of questions