Turning Effect & Center of mass

The diagram shows an object of weight W and an object of weight Z balanced on a uniform metre

rule.

Which equation relating to W, Z, a and b is correct?

• ( W / a ) = ( Z / b )

• W x Z = a x b

• W x a = Z x b

• W x ( a + b) = Z

The diagrams show four objects A, B, C and D. The centre of mass M of each object is marked

on the diagrams.

Which object is not in equilibrium?

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Five identical bags of rice are balanced on a uniform beam by an object of mass 10 kg.

Two more identical bags of rice are added to the other five. The average position of the bags on the beam does not change.

What mass now balances the bags?

• 3.5 kg

• 7.0 kg

• 12 kg

• 14 kg

The diagram shows an unbalanced rod. Two loads X and Y can be moved along the rod.

The rod turns in a clockwise direction as shown.

Which action could make the rod balance?

• moving X to the left

• moving X to the right

• moving Y to the right

• moving the pivot to the left

The diagram shows a balance being used to find the weight of a baby. The weight of the basket can be ignored.

At equilibrium, the pivot is nearer to the 40 N balancing weight than to the baby.

What is the weight of the baby?

• less than 40 N

• 40 N

• more than 40 N

• impossible to tell without a scale on the beam

The diagram shows a uniform beam being used as a balance. The beam is pivoted at its centre.

A 1.0 N weight is attached to one end of the beam. An empty pan weighing 0.2 N is attached to the other end of the beam.

How many 0.1 N weights must be placed on the pan in order to balance the beam?

• 5

• 8

• 10

• 12

A heavy beam rests on two supports. The diagram shows the only three forces F1, F2 and F3 acting on the beam.

The beam is in equilibrium.

Which statement is correct?

• All the forces are equal in size.

• The resultant force on the beam is in the opposite direction to the resultant turning effect.

• The resultant force on the beam is zero and the resultant turning effect on the beam is zero.

• The total upward force is twice the total downward force.

The diagrams show four solid cones. The centre of mass of each cone is marked by a point labelled M.

Which cone is the most stable?

• A

• B

• C

• D

A heavy truck on wheels has a platform attached to it.

A man stands on the platform.

The truck does not fall over.

Which position A, B, C or D could be the centre of mass of the whole system (truck, platform and

man)?

• A

• B

• C

• D

A uniform rod rests on a pivot at its centre. The rod is not attached to the pivot. Forces are then applied to the rod in four different ways, as shown. The weight of the rod can be ignored.

Which diagram shows the rod in equilibrium?

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