Moments Practice Questions

Question 1

4 marks

Figure 1 shows a rod that can turn about an axle. Four forces, P, Q, R and S, act on the rod.

(a)

Which force will make the rod turn about the axle?

A P
B Q
C R
D S

/ 1

(b)

State the direction in which the rod will turn.

/ 1

(c)

Describe one everyday situation in which a force causes an object to rotate about a pivot. Identify the force and the pivot in your answer.

/ 2

Question 2

4 marks

A mechanic uses a spanner to turn a bolt. She applies a force of $45$ N at right angles to the spanner, at a distance of $0.22$ m from the centre of the bolt.

(a)

Calculate the moment of this force about the centre of the bolt.

Give the unit.

moment = ...............................................

/ 2

(b)

The bolt is rusty. A moment of at least $14$ N m is needed to turn it.

Calculate the smallest force the mechanic must apply at the same distance of $0.22$ m to turn the bolt.

force = ............................................... N

/ 2

Question 3

4 marks

Two students sit on a seesaw. The seesaw is balanced horizontally, as shown in Figure 2.

Ella has a weight of $320$ N and sits $1.5$ m from the pivot.
Ben sits $2.0$ m from the pivot on the other side.

Diagram not drawn to scale.

(a)

State the principle of moments.

/ 1

(b)

Calculate Ben's weight.

weight = ............................................... N

/ 3

Question 0

5 marks

Figure 3 shows a loaded wheelbarrow. The wheelbarrow acts as a lever, with the wheel as the pivot.

The load has a weight of $400$ N. Its weight acts $0.40$ m from the wheel.
The gardener lifts the handles by applying a vertical force $1.20$ m from the wheel.

The weight of the wheelbarrow itself can be ignored.

(a)

Calculate the force the gardener must apply to the handles to just lift the load.

force = ............................................... N

/ 3

(b)

Explain, in terms of moments, why the force applied by the gardener is smaller than the weight of the load.

/ 2

Question 0

5 marks

A hand drill contains two meshed gear wheels. The handle turns gear A, which has $48$ teeth. Gear A turns gear B, which has $16$ teeth. The drill bit is attached to gear B.

(a)

Gear A turns clockwise. State the direction in which gear B turns.

/ 1

(b)

Gear A turns $4$ times each second.

Calculate the number of times gear B turns each second.

number of turns each second = ...............................................

/ 2

(c)

Explain why the turning effect produced at the drill bit is smaller than the turning effect applied to gear A.

/ 2

Question 0

5 marks

Figure 4 shows a tower crane. The jib can turn about the top of the tower.

A load of weight $5000$ N hangs $12$ m from the tower. A concrete counterweight of weight $15\,000$ N hangs on the other side, a distance $d$ from the tower. The jib is horizontal and in equilibrium.

Diagram not drawn to scale.

(a)

Calculate the distance $d$ .

$d$ = ............................................... m

/ 3

(b)

The same load is now moved out to $16$ m from the tower. The counterweight is not moved.

State and explain what happens to the jib.

/ 2

Question 0

5 marks

A full wheelie bin is standing upright on level ground. To move it, a person pulls horizontally on the handle. The bin will start to tip about the axle of the wheels.

The weight of the bin and its contents is $250$ N. This weight acts through a line that is $0.30$ m horizontally from the axle.
The person pulls with a horizontal force of $60$ N. The handle is $0.95$ m vertically above the axle.

(a)

Explain, using calculations, why the bin does not tip.

/ 3

(b)

Suggest one change the person could make so that the bin tips, and explain why it works.

/ 2

Question 0

6 marks

Figure 5 shows a mobile made from a light rod hanging from a thread tied to the centre of the rod. Four decorations hang from the rod. The mobile is in equilibrium and the rod is horizontal.

Diagram not drawn to scale.

(a)

Use the principle of moments to calculate the distance $d$ of the $50$ g decoration from the centre of the rod.

$d$ = ............................................... cm

/ 4

(b)

The $50$ g decoration is now moved so that it hangs $20$ cm from the centre of the rod. Nothing else is changed.

State and explain what happens to the rod.

/ 2

Question 0

6 marks

A cyclist pushes vertically downwards on a pedal with a force of $320$ N. The pedal is attached to a crank of length $0.17$ m, which turns about the axle of the chain wheel.

(a)

Calculate the moment of this force about the axle when the crank is horizontal.

moment = ............................................... N m

/ 2

(b)

As the crank turns away from the horizontal position, the cyclist keeps pushing vertically downwards with the same force of $320$ N. The moment produced about the axle becomes smaller.

Explain why.

/ 2

(c)

At one point in the turn, the perpendicular distance from the axle to the line of action of the cyclist's force is $0.085$ m.

To keep climbing the hill, a moment of $48$ N m is needed at this point.

Calculate the force the cyclist must apply.

force = ............................................... N

/ 2

Key Concepts of Physics

Motion & Forces

Conservation of Energy

Waves

Light & the Electromagnetic Spectrum

Radioactivity

Astronomy

Energy – Forces Doing Work

Forces & their Effects

Electricity & Circuits

Static Electricity

Magnetism & the Motor Effect

Electromagnetic Induction

Particle Model

Forces & Matter

Question 1

Question 2

Question 3

Question 0

Question 0

Question 0

Question 0

Question 0

Question 0