THE TURNING EFFECT OF FORCES
4 marks · NormalA person tries to open a heavy gate by applying a force of 120 N perpendicular to the gate, 0.75 m from the hinge. Another person tries to keep the gate closed by pushing with a force of 180 N, but only 0.3 m from the hinge.
Calculate the moment produced by the first person about the hinge.
Calculate the moment produced by the second person about the hinge.
State which person has a greater turning effect on the gate and explain your answer.
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(a) 90 Nm
(b) 54 Nm
(c) The first person has a greater turning effect because their moment (90 Nm) is greater than the second person's moment (54 Nm), due to either a larger force or applying it further from the hinge. · must show Reference to moments being greater, Reasoning based on calculation
Common mistakes: Using non-perpendicular distance; Multiplying wrong pairs of force and distance
Show mark scheme and worked solution
Marking points
M1 (a) · 0.5 marks · Correct substitution into moment = force × distance
A1 (a) · 0.5 marks · Correct calculation: 120 × 0.75 = 90 Nm
M2 (b) · 0.5 marks · Correct substitution for second person
A2 (b) · 0.5 marks · 180 × 0.3 = 54 Nm
B1 (c) · 1 mark · Correctly identifies first person as having greater turning effect (follow-through)
B2 (c) · 1 mark · Explanation relates to moments and gives valid reasoning based on calculation
Worked solution
a) Moment = force × perpendicular distance: 120 N × 0.75 m = 90 Nm.
b) Moment = 180 N × 0.3 m = 54 Nm.
c) The first person creates a greater turning effect (90 Nm > 54 Nm), so their force will have a greater effect in opening the gate. This is because the larger distance from the pivot or the size of the force increases the moment.