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4.2. Equilibrium of forces
A subsection of Physics, 9702, through 4. Forces, density and pressure
Listing 10 of 113 questions
Define the moment of a force about a point. Determine the SI base units of the moment of a force. base units A uniform rigid rod of length 2.4 m is shown in . 2.4 m cross-sectional area A The rod has a weight of 5.2 N and is made of wood of density 790 kg m–3. Calculate the cross-sectional area A, in mm2, of the rod. A = mm2 A fishing rod AB, made from the rod in , is shown in . 4.6 N B C T D A 1.20 m 56° 0.60 m 0.60 m string ground weight 5.2 N water stick (not to scale) End A of the rod rests on the ground and a string is attached to the other end B. A support stick exerts a force perpendicular to the rod at point C. The weight of the rod acts at point D. The tension T in the string is in a direction perpendicular to the rod. The rod is in equilibrium and inclined at an angle of 56° to the vertical. The forces and the distances along the rod of points A, B, C and D are shown in . Show that the component of the weight that is perpendicular to the rod is 4.3 N. By taking moments about end A of the rod, calculate the tension T. T = N
9702_w20_qp_21
THEORY
2020
Paper 2, Variant 1
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A rigid plank is used to make a ramp between two different horizontal levels of ground, as shown in . 45 N 96 N rope B A D C T 38° 1.10 m 1.50 m 0.30 m (not to scale) Point A at one end of the plank rests on the lower level of the ground. A force acts on, and is perpendicular to, the plank at point B. The plank is held in equilibrium by a rope that connects point D on the plank to the ground. The plank has a weight that may be considered to act from its centre of gravity C. The rope is perpendicular to the plank and has tension T. The plank is at an angle of 38° to the vertical. The forces and the distances along the plank of points A, B, C and D are shown in . Show that the component of the weight that is perpendicular to the plank is 59 N. By taking moments about end A of the plank, calculate the tension T. T = N
9702_w20_qp_22
THEORY
2020
Paper 2, Variant 2
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State what is meant by the centre of gravity of a body. A uniform wooden post AB of weight 45 N stands in equilibrium on hard ground, as shown in . T B C A 60° 0.30 m 0.90 m horizontal 45 N 38 N ground (not to scale) End A of the vertical post is supported by the ground. A horizontal wire with tension T is attached to end B of the post. Another wire, attached to the post at point C, is at an angle of 60° to the horizontal and has tension 38 N. The distances along the post of points A, B and C are shown in . Calculate the horizontal component of the force exerted on the post by the wire connected to point C. horizontal component of force = N By considering moments about end A, determine the tension T. T = N Calculate the vertical component of the force exerted on the post at end A. force = N
9702_w20_qp_23
THEORY
2020
Paper 2, Variant 3
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Questions Discovered
113