A uniform plank of wood is pivoted at its centre. A block of wood of mass 2kg is balanced by a mass of 1.5 placed...

A uniform plank of wood is pivoted at its centre. A block of wood of mass 2kg is balanced by a mass of 1.5 placed 30cm from the pivot as shown.


i) Calculate the distance X
ii) When the same block of wood is partially immersed in water, the 1.5kg mass need to be placed at 20cm from the pivot to balance it. Calculate the weight of the water displaced.

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(i)
Clockwise moments = Anticlockwise moment.
2.0g x = 1.5g x 30
2x = 45
x = 22.5cm

(ii)
Down force: M x 22.5
= 20 x 1.5
M = 30/22.5 = 1.33Kg
Upthrust = 0.67Kg.

Therefore weight of water displaced = 6.7N

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Wilfykil answered the question on March 27, 2019 at 07:11

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