Deformation

A wire is stretched by 8 mm when a load of 60 N is applied. What will be the extension of a wire of the same material having four times the cross-sectional area and twice the original length, when the same load is applied?

• 2 mm

• 4 mm

• 8 mm

• 16 mm

What is plastic deformation?

• Plastic deformation occurs when extension is not proportional to force but when the load is removed the material returns to its original length

• Plastic deformation occurs if, when the load is removed, the material contracts but a permanent stretching has occurred.

• Plastic deformation occurs until the extension is no longer proportional to the load.

• Plastic deformation occurs when the material extends so that elongation is directly proportional to the load.

A piece of copper is drawn into a continuous wire. What behaviour is the copper exhibiting?

• brittle only

• elastic only

• plastic only

• both brittle and elastic

A sample of metal is subjected to a force which increases to a maximum value and then decreases back to zero.

A force-extension graph for the sample is shown.

When the sample contracts it follows the same force-extension curve as when it was being stretched. What is the behaviour of the metal between X and Y?

• both elastic and plastic

• elastic but not plastic

• plastic but not elastic

• not elastic and not plastic

A simple crane consists of a rigid vertical pillar supporting a horizontal beam.

A weight W is lifted by a rope at the end of the beam. What are the forces at points X, Y and Z due to the weight W?

• force at X - tension; force at Y - compression; force at Z - tension

• force at X - tension; force at Y -tension; force at Z - compression

• force at X - compression; force at Y -tension; force at Z - compression

• force at X - compression; force at Y -compression; force at Z - compression

Which row best defines elastic and plastic behaviour of a material?

• elastic behaviour of a material - extends only within the limit of proportionality; plastic behaviour of a material - extends beyond the limit of proportionality

• elastic behaviour of a material - has a linear force-extension curve ; plastic behaviour of a material - has a horizontal force-extension curve

• elastic behaviour of a material - obeys Hooke’s Law; plastic behaviour of a material - extends continuously under a steady load

• elastic behaviour of a material - returns to its original shape; plastic behaviour of a material - suffers permanent deformation and size

Four materials are formed into rods of the same dimensions. At room

temperature, which can sustain the largest plastic deformation?

• the ductile material aluminium

• the brittle material carbon

• the brittle material glass

• the ductile material steel

1.      Two steel wires P and Q have lengths l and 2l respectively, and cross-sectional areas A and A/2 respectively. Both wires obey Hooke’s law.

What is the ratio  tension 'P/ tension Q'  when both wires are stretched to the same extension?

 $\frac{tension\ P}{tension\ Q}$  

•  $\frac{1}{4}$  

•  $\frac{1}{2}$  

•  $\frac{2}{1}$  

•  $\frac{4}{1}$  

A spring is compressed by a force. The graph shows the compressing force F plotted against the length L of the spring.

What is the spring constant of this spring?

• 0.2 N m^–1

• 5 N m^–1

• 100 N m^–1

• 200 N m^–1