Turning Effect of Force
10 Grade 10 General Science questions on Turning Effect of Force, with worked marking schemes. 10 questions are available on this topic in full.
Question 1
6 marksAt a playground, Achieng, who weighs 400 N, sits 1.5 m from the pivot of a seesaw. The plank is uniform and pivoted at its centre. Otieno weighs 500 N.
(a) Calculate how far from the pivot, on the other side, Otieno must sit for the seesaw to balance horizontally. (3 marks)
(b) Achieng's younger brother, who weighs 200 N, then sits on Achieng's side at 0.9 m from the pivot. Calculate the new distance from the pivot at which Otieno must sit to balance the seesaw. (3 marks)
(6 marks)
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1 markCarpenters in a Kisumu workshop always fit door handles at the edge of the door farthest from the hinges. What is the reason for this?
A. The pushing force passes closer to the pivot line
B. The hinges then carry less of the weight of the door
C. The door becomes lighter when pushed far from hinges
D. A smaller force produces the turning moment needed
(1 mark)
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4 marksDuring a class activity, a uniform metre rule is pivoted at the 30 cm mark. It balances horizontally when a 2 N weight is hung at the 5 cm mark.
(a) Calculate the weight of the metre rule. (3 marks)
(b) Determine the mass of the metre rule. (Take g = 10 N/kg) (1 mark)
(4 marks)
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1 markKamau uses a spanner 25 cm long to loosen a wheel nut on a tractor. He applies a force of 40 N at the end of the spanner, perpendicular to it. What is the moment of the force about the nut?
A. 10 N m
B. 160 N m
C. 1000 N m
D. 1.6 N m
(1 mark)
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3 marks(a) Define the moment of a force about a point. (1 mark)
(b) A watchman at a school gate in Machakos opens a heavy gate by pushing with a force of 120 N at a perpendicular distance of 1.5 m from the hinge. Calculate the moment of the force about the hinge. (2 marks)
(3 marks)
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1 markChebet is riding a bicycle. When a pedal crank points vertically downwards, pushing straight down on that pedal does not turn the crank at all. Why is this so?
A. Her weight is too small to turn the crank
B. The chain is slack at that position of the pedal
C. The force acts at the greatest distance from the axle
D. The line of the force passes through the axle
(1 mark)
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4 marksDuring a walk around the school compound, Grade 10 learners observed a carpenter pulling stubborn nails out of timber with a long-handled claw hammer, and a tailor cutting thick fabric by placing it close to the pivot of a pair of scissors. Using the idea of the turning effect of a force, explain why:
(a) the long-handled claw hammer removes a stubborn nail easily; (2 marks)
(b) thick fabric is cut more easily when placed close to the pivot of the scissors. (2 marks)
(4 marks)
Marking scheme
(a) (2 marks) - The hammer acts as a lever turning about the point where its head rests on the timber (the pivot). (1) - The long handle gives a large perpendicular distance between the effort and the pivot, so a small effort produces a large moment, which exerts a large force on the nail that is close to the pivot. (1) (b) (2 marks) - The fabric near the pivot is at a small distance from the pivot, while the effort at the handles is at a larger distance. (1) - Since the moment of the effort equals the moment of the force on the fabric, a small distance gives a large cutting force on the fabric. (1)
Question 8
1 markA tower crane at a building site in Nairobi has a heavy concrete block fixed at the end of its arm, on the side opposite the hook that carries the load. What is the main purpose of the concrete block?
A. To increase the height the load can be raised to
B. To make the arm turn faster when swinging round
C. To balance the load's moment about the tower
D. To reduce the weight of the load on the hook
(1 mark)
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1 markA plumber turns a stiff tap by pressing on the two ends of its handle with equal forces acting in opposite directions. What is the effect of these two forces on the tap?
A. It stays at rest since the forces cancel out
B. It rotates without being moved sideways
C. It rotates and also slides along the handle
D. It moves sideways along one of the forces
(1 mark)
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5 marksYou are provided with a metre rule, a knife edge, some thread and two different known masses. Describe how you would use this apparatus to verify the principle of moments. (5 marks)
(5 marks)
Marking scheme
Any five of the following, 1 mark each (5 marks): - Balance the metre rule alone on the knife edge and note the balance point (its centre of gravity, about the 50 cm mark); keep the pivot at this point. - Hang the first mass (m₁) with thread at a fixed distance d₁ on one side of the pivot. - Hang the second mass (m₂) on the other side and adjust its position until the rule balances horizontally. - Measure the distances d₁ and d₂ of the masses from the pivot. - Calculate the moments W₁ × d₁ and W₂ × d₂ (or m₁g × d₁ and m₂g × d₂). - Repeat for several different positions of the first mass and record the results. - Observation/conclusion: in each case the anticlockwise moment is equal to the clockwise moment (within experimental error), which verifies the principle.
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