4.3 Turning effects of forces 2021-2023 IG

A force F acts on an object at a distance x from a pivot.

Which two changes both increase the moment of the force about the pivot?

(a)  

The diagram shows a uniform rod with its midpoint on a pivot. Two weights X and Y are hung from the rod.

The rod is in equilibrium.

Which statement is correct?

• The forces at X and Y have different values.

• There is a resultant turning effect on the rod.

• The resultant force on the rod is zero.

• The rod does not have a centre of mass.

What is the unit for the moment of a force about a point?

• W

• Ns

• N/m

• Nm

A spanner is used to tighten a nut on a bicycle wheel.

A force F is needed.

How can the force F be reduced?

• Use a longer handle.

• Use a shorter handle.

• Use a thinner handle.

• Use a thicker handle.

A wheelbarrow has a weight W of 140 N.

Which vertical force F is needed to support the wheelbarrow in the position shown?

• 60 N

• 80 N

• 140 N

• 245 N

The diagram shows a metre rule MN on two supports, P and Q. Two loads are placed on the rule, as shown. The rule rests steadily on the supports.

Which row is correct?

• total moment about M is clockwise, total moment about N is anticlockwise

• total moment about M is clockwise, total moment about N is zero

• total moment about M is zero, total moment about N is clockwise

• total moment about M is zero, total moment about N is zero

A metal rod of length 80 cm is pivoted at point O. Its centre of mass is at its mid-point. Four pulley wheels are indicated by the letter P. (Refer to the diagram.) The rod is in equilibrium, as shown.

What is the weight of the rod?

• 0.20 N

• 1.0 N

• 2.0 N

• 4.0 N

A beam is pivoted at one end. The beam weighs 6.0 N and its weight acts at a point X 40 cm from the pivot. A force of 4.0 N is applied to the beam causing it to balance horizontally.

In which direction and where is the 4.0 N force applied?

• vertically downwards at 20 cm to the left of X

• vertically downwards at 20 cm to the right of X

• vertically upwards at 20 cm to the left of X

• vertically upwards at 20 cm to the right of X

What are the conditions for an object to be in equilibrium?

• no resultant force, no resultant moment

• no resultant force, resultant moment

• resultant force, no resultant moment

• resultant force, resultant moment

The diagram shows two identical bars of negligible weight.

All the forces acting on each bar are marked.

Which bars are in equilibrium?

• bar 1 and bar 2

• bar 1 only

• bar 2 only

• neither bar 1 nor bar 2