class 7 hookes law - mr. gopie class - home2mm!=!5/5!x!2! ... june!2000!paper!2!#!1!! mr!r!gopie ......
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PHYSICS Hooke`s Law
Mr Rishi Gopie
Mr R Gopie PHYSICS
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DEFORMING EFFECTS OF A FORCE
HOOKES LAW
When a tensile (i.e. stretching) force is applied to a specimen of material it may produce an extension (i.e. an increase in length) of the specimen. Hooke`s law states that once the elstic limit of the material in not exceeded then the applied force (F) is directly proportional to the extension (e) , i.e. F α e the law can be investigated using springs and elastic bands ( such as rubber bands)
Up to the elastic limit the material is said to be elastic and this means that when the force is removed the specimen returns to its original dimensions. Beyond the elastic limit the material is said to be plastic and this means that when the force is removed the specimen will not return to its original dimensions
Consider a typical force –extension graph.
Diag. 1
Mr R Gopie PHYSICS
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Consider an example
When a mass of 500g is hung from a spring it produces an extension of 5mm. Assuming that in all cases Hooke`s law is obeyed
a) What mass will produce an extension of 1.5mm? b) What weight will produce an extension of 2mm? c) What extension will be caused by a mass of 200g? d) What extension will be caused by a weight of 8N?
a) Since 5mm extension is caused by a mass of 500g then 1mm ext. will be 500g/5 = 100g
Therefore 1.5mm ext. = 100 x 1.5 = 150g
b) Weight = m x g So 500g = 5N = 0.5kg x 10Nkg = 5N Since 5mm ext. is caused by a weight of 5N The 1 will be 5/5N Therefore 2mm = 5/5 x 2 = 2N
c) Since 500g causes an extension of 5mm 1g will cause 5/500 Therefore 200g will cause = 5/500 x 200/1 = 2mm
d) A mass of 500g has a weight of 5N and a weight of 5N causes an extension of 5mm 1N will cause 5/5mm Therefore 8N will cause (5/5 x8) mm = 8mm.
Mr R Gopie PHYSICS
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TUTORIAL June 2000 paper 2 # 1
Mr R Gopie PHYSICS
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Mr R Gopie PHYSICS
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