Monday 6 May 2013

Test Yourself Mark Scheme - Moments & Hydraulics


(a)   1 Liquids are virtually incompressible. 
       2 Pressure is transmitted equally in all directions throughout a liquid. 
 Both of the properties have been expressed clearly and concisely. In the first answer if the word ‘virtually’ had been omitted the mark would still have been given. If you forget the word ‘incompressible’ you could say ‘cannot be squashed’.

(b)    2 ´ 105 N 3
 ome of the data have been given in standard form. You can leave them like this and give an answer in standard form or rewrite 8 ´ 106 as 8 000 000 and give the answer as 200 000 N. However, for some questions, mainly those involving very big or very small numbers, you should understand and be able to use standard form.

(c)   If the maximum weight were exceeded the moments would no longer balance. The resultant moment would cause the crane to topple. 
Although it is not clear if it is the whole crane or just the jib that would topple, the marks have been given for the idea that a resultant moment will cause something to rotate.

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