Physics 9702 · Paper 2

Forces, Density & Pressure

Definitions: Forces, Density & Pressure

One exam question, the mark-scheme answer, and the exact phrases that score (highlighted, then listed below in the same colour).

Exam question

Define the moment of a force.

1 mark

Model answer

The moment of a force is the force × the perpendicular distance of the line of action of the force from the point.

Marking points

1 mark each

1force × the perpendicular distance of the line of action of the force from the point(1)

Exam question

State what is meant by a couple.

1 mark

Model answer

A couple is two equal, opposite, parallel forces that are not in line.

Marking points

1 mark each

1two equal, opposite, parallel forces that are not in line(1)

Exam question

Define the torque of a couple.

1 mark

Model answer

The torque of a couple is one force × the perpendicular distance between the forces.

Marking points

1 mark each

1one force × the perpendicular distance between the forces(1)

Exam question

Define the centre of gravity of an object.

1 mark

Model answer

The centre of gravity is the point where all the weight of the object may be considered to act.

Marking points

1 mark each

1point where all the weight of the object may be considered to act(1)

Exam question

State the principle of moments.

2 marks

Model answer

For an object in equilibrium, the sum of the clockwise moments about a point equals the sum of the anticlockwise moments about the same point.

Marking points

1 mark each

1in equilibrium(1)
2clockwise moments about a point equals the sum of the anticlockwise moments about the same point(1)

Exam question

State the conditions for an object to be in equilibrium.

2 marks

Model answer

An object is in equilibrium when the resultant force is zero and the resultant moment about any point is zero.

Marking points

1 mark each

1resultant force is zero(1)
2resultant moment about any point is zero(1)

Exam question

Define density.

1 mark

Model answer

Density is mass per unit volume.

Marking points

1 mark each

1mass per unit volume(1)

Exam question

Define pressure.

1 mark

Model answer

Pressure is force per unit area (normal to the area).

Marking points

1 mark each

1force per unit area (normal to the area)(1)

Exam question

Explain how upthrust arises on an object in a fluid.

2 marks

Model answer

Pressure in the fluid increases with depth, so the force on the bottom surface is greater than the force on the top.

Marking points

1 mark each

1increases with depth(1)
2force on the bottom surface is greater than the force on the top(1)

PreviousDynamics NextWork, Energy & Power

Physics 9702 · Paper 2

Forces, Density & Pressure

Definitions: Forces, Density & Pressure

One exam question, the mark-scheme answer, and the exact phrases that score (highlighted, then listed below in the same colour).

Exam question

Define the moment of a force.

1 mark

Model answer

The moment of a force is the force × the perpendicular distance of the line of action of the force from the point.

Marking points

1 mark each

1force × the perpendicular distance of the line of action of the force from the point(1)

Exam question

State what is meant by a couple.

1 mark

Model answer

A couple is two equal, opposite, parallel forces that are not in line.

Marking points

1 mark each

1two equal, opposite, parallel forces that are not in line(1)

Exam question

Define the torque of a couple.

1 mark

Model answer

The torque of a couple is one force × the perpendicular distance between the forces.

Marking points

1 mark each

1one force × the perpendicular distance between the forces(1)

Exam question

Define the centre of gravity of an object.

1 mark

Model answer

The centre of gravity is the point where all the weight of the object may be considered to act.

Marking points

1 mark each

1point where all the weight of the object may be considered to act(1)

Exam question

State the principle of moments.

2 marks

Model answer

For an object in equilibrium, the sum of the clockwise moments about a point equals the sum of the anticlockwise moments about the same point.

Marking points

1 mark each

1in equilibrium(1)
2clockwise moments about a point equals the sum of the anticlockwise moments about the same point(1)

Exam question

State the conditions for an object to be in equilibrium.

2 marks

Model answer

An object is in equilibrium when the resultant force is zero and the resultant moment about any point is zero.

Marking points

1 mark each

1resultant force is zero(1)
2resultant moment about any point is zero(1)

Exam question

Define density.

1 mark

Model answer

Density is mass per unit volume.

Marking points

1 mark each

1mass per unit volume(1)

Exam question

Define pressure.

1 mark

Model answer

Pressure is force per unit area (normal to the area).

Marking points

1 mark each

1force per unit area (normal to the area)(1)

Exam question

Explain how upthrust arises on an object in a fluid.

2 marks

Model answer

Pressure in the fluid increases with depth, so the force on the bottom surface is greater than the force on the top.

Marking points

1 mark each

1increases with depth(1)
2force on the bottom surface is greater than the force on the top(1)

PreviousDynamics NextWork, Energy & Power