1.5.5. Turning effect of forces
A subsection of Physics, 5054, through 1. Motion, forces and energy
Listing 10 of 30 questions
State what is meant by the moment of a force. The anchor of a sailing ship has a mass of 350 kg. Six sailors raise the anchor from the sea-bed by turning a large axle. They push the handles attached to the axle and it rotates. The anchor is on the end of a chain that winds on to the rotating axle. shows the sailors lifting the anchor. handle axis of rotation 1.2 m axle chain to anchor Each of the sailors exerts a force of 750 N on his handle at a distance of 1.2 m from the axis of rotation. The axle rotates through one complete revolution and the anchor is lifted through a distance of 160 cm. The gravitational field strength g is 10 N / kg. Calculate 1. the total moment exerted on the axle by the six sailors, moment = 2. the gravitational potential energy gained by the anchor as the axle rotates through one complete revolution. energy = The work done on the axle by the sailors is very much larger than the gravitational potential energy gained by the anchor. State and explain how energy is wasted. Explain why the power produced by the sailors is larger when the anchor is lifted at a faster rate. Describe, with the aid of a labelled diagram, how to verify the principle of moments.
5054_w13_qp_22
THEORY
2013
Paper 2, Variant 2
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In hospitals, doctors and nurses operate taps with their elbows in order to avoid contamination. shows a hospital tap with a long handle. 0.18 m X handle A nurse applies a force of 2.5 N at a point X on the handle, 0.18 m from the axis of the tap. Calculate the maximum moment about the axis that this force can produce. moment = The moment produced by the nurse is less than this maximum value. Suggest one reason why this is so. State how the force needed to operate the tap is affected by the length of the handle.
5054_w14_qp_22
THEORY
2014
Paper 2, Variant 2
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shows a door and an automatic door-closer viewed from above. point X door bar bar fixed to wall hinge door closer 0.72 m P F When the door opens and closes, the hinge acts as a pivot. A girl opens the door by exerting a force P at point X. Force P is perpendicular to the surface of the door. shows that point X is a distance of 0.72 m along the front of the door from the hinge. The force P is 25 N. Calculate the moment of force P about the hinge. moment of force = The door rotates about the hinge by 90°. The circumference of a circle of radius 0.72 m is 4.5 m. Calculate the work done on the door by force P. work done = As the door opens, there is a force F on the door in the direction shown in . Although force F is larger than force P, the door rotates about the hinge. Explain why.
5054_w20_qp_21
THEORY
2020
Paper 2, Variant 1
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The turning effect of a force is measured by its moment. shows a force F acting on an object at point P. The object is free to rotate about an axis at X that is perpendicular to the page. F X object P Write down an expression for the moment of F about the axis at X. Draw on to show what is meant by any other term used in your expression. State the principle of moments. Describe an experiment to verify the principle of moments. Include a diagram to help the description. A worker carries a ladder on his shoulder. His shoulder acts as a pivot. shows that the ladder is horizontal. centre of mass 0.90 m 0.54 m 1.3 m bucket ladder L The ladder is wider at one end than at the other end. The mass of the ladder is 8.0 kg. The gravitational field strength is 10 N / kg. Calculate the weight of the ladder. weight = State what is meant by centre of mass. The centre of mass of the ladder is not halfway along its length. State what this shows about the ladder. The centre of mass of the ladder is a horizontal distance of 0.90 m from the worker’s shoulder. Calculate the moment about the worker’s shoulder of the weight of the ladder. moment = A bucket of weight 87 N is suspended from the ladder at a horizontal distance of 1.3 m from the worker’s shoulder. The worker keeps the ladder horizontal by exerting a vertical force at point L. L is a horizontal distance of 0.54 m from his shoulder. Determine the size and direction of the force exerted at L. size of force = direction =
5054_w21_qp_22
THEORY
2021
Paper 2, Variant 2
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Questions Discovered
30