SEC 3 Physics Quiz For SST Students - Moment

1. Victor and Jerry want to play see-saw. Victor is twice as heavy as Jerry. If they want the see-saw to balance easily, how far should they sit from the fulcrum?

They should sit at the same distance from the fulcrum.

Victor’s distance from the fulcrum should be twice as far as Jerry’s

Victor’s distance from the fulcrum should be half as far as Jerry’s.

Victor’s distance from the fulcrum should be four times as far as Jerry’s.

If Victor is twice as heavy as Jerry, in order for the see-saw to balance easily, Victor's distance from the fulcrum should be half as far as Jerry's. This is because the torque (or turning force) exerted by each person on the see-saw is equal to their weight multiplied by their distance from the fulcrum. Since Victor is twice as heavy, his torque is already twice as much as Jerry's. Therefore, to balance the see-saw, Victor needs to sit closer to the fulcrum so that his smaller torque is compensated by the larger distance.

Explanation

If Victor is twice as heavy as Jerry, in order for the see-saw to balance easily, Victor's distance from the fulcrum should be half as far as Jerry's. This is because the torque (or turning force) exerted by each person on the see-saw is equal to their weight multiplied by their distance from the fulcrum. Since Victor is twice as heavy, his torque is already twice as much as Jerry's. Therefore, to balance the see-saw, Victor needs to sit closer to the fulcrum so that his smaller torque is compensated by the larger distance.

2. The diagram below shows a man of weight 800N standing in the middle of a uniform, rigid, horizontal plank. The plank weighs 1 000N. Which one of the following diagrams shows the force on the plank?

A

B

C

D

In diagram A, the man exerts a downward force of 800N due to his weight, and the plank exerts an equal and opposite upward force of 800N on the man according to Newton's third law. Additionally, the plank exerts a downward force of 1000N due to its weight. Therefore, the net force on the plank is 1000N downward. This is the correct representation of the forces on the plank.

Explanation

In diagram A, the man exerts a downward force of 800N due to his weight, and the plank exerts an equal and opposite upward force of 800N on the man according to Newton's third law. Additionally, the plank exerts a downward force of 1000N due to its weight. Therefore, the net force on the plank is 1000N downward. This is the correct representation of the forces on the plank.

3. The diagrams below show a lorry carrying different loads of the same mass. Which one of the following diagrams shows that the lorry is the most stable?

A

B

C

D

Diagram B shows that the lorry is the most stable because the load is distributed evenly on both sides of the lorry. This creates a balanced and symmetrical arrangement, reducing the chances of tipping over. In contrast, the other diagrams show uneven distribution of the load, which can lead to instability and a higher risk of tipping.

Explanation

Diagram B shows that the lorry is the most stable because the load is distributed evenly on both sides of the lorry. This creates a balanced and symmetrical arrangement, reducing the chances of tipping over. In contrast, the other diagrams show uneven distribution of the load, which can lead to instability and a higher risk of tipping.

4. The diagram shows the use of a lever. If OP = 10 cm, PQ = 20 cm and Load = 50N. What is the minimum effort required to lift the load?

50 N

100 N

150 N

200 N

The lever is a simple machine that allows for the amplification of force. In this diagram, the effort is applied at point O and the load is at point Q. The lever arm OP is 10 cm and the lever arm PQ is 20 cm. The lever arm is the perpendicular distance between the line of action of the force and the pivot point. To find the minimum effort required to lift the load, we can use the principle of moments. The moment of the effort is equal to the moment of the load. Therefore, the effort multiplied by the lever arm OP is equal to the load multiplied by the lever arm PQ. So, Effort x 10 cm = 50 N x 20 cm. Solving for the effort, we get Effort = (50 N x 20 cm) / 10 cm = 100 N. Therefore, the minimum effort required to lift the load is 100 N.

Explanation

The lever is a simple machine that allows for the amplification of force. In this diagram, the effort is applied at point O and the load is at point Q. The lever arm OP is 10 cm and the lever arm PQ is 20 cm. The lever arm is the perpendicular distance between the line of action of the force and the pivot point. To find the minimum effort required to lift the load, we can use the principle of moments. The moment of the effort is equal to the moment of the load. Therefore, the effort multiplied by the lever arm OP is equal to the load multiplied by the lever arm PQ. So, Effort x 10 cm = 50 N x 20 cm. Solving for the effort, we get Effort = (50 N x 20 cm) / 10 cm = 100 N. Therefore, the minimum effort required to lift the load is 100 N.

5. Which of the following shows a sphere in stable equilibrium?

A

B

C

D

Option C shows a sphere in stable equilibrium because its center of gravity is located at the lowest point of the sphere. In stable equilibrium, if the sphere is slightly displaced from its equilibrium position, it will experience a restoring force that brings it back to the original position. This is because the center of gravity is directly below the pivot point, ensuring stability.

Explanation

Option C shows a sphere in stable equilibrium because its center of gravity is located at the lowest point of the sphere. In stable equilibrium, if the sphere is slightly displaced from its equilibrium position, it will experience a restoring force that brings it back to the original position. This is because the center of gravity is directly below the pivot point, ensuring stability.

6. The figure below shows a rigid bar pivoted at O. There are four forces acting on the bar at various positions.

Calculate the total clockwise moment about O.

The total clockwise moment about point O can be calculated by summing up the individual moments caused by each force. Since the question does not provide any specific values for the forces or their positions, it is not possible to determine the exact calculation. However, based on the given answer choices, it can be concluded that the total clockwise moment about O is 22 Nm or 22 Newton meters.

Explanation

The total clockwise moment about point O can be calculated by summing up the individual moments caused by each force. Since the question does not provide any specific values for the forces or their positions, it is not possible to determine the exact calculation. However, based on the given answer choices, it can be concluded that the total clockwise moment about O is 22 Nm or 22 Newton meters.

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