A graduated plank of length 90cm sits on a knife edge at 40cm mark. When a load of 50g is placed at 20cm, find the mass that will balance the plank at 70cm length.

33.3 g ≈ 33 g

Explanation:

Please see attached photo for explanation.

From the attached photo, M is the mass that we must obtain to balance the plank.

The mass, M can be obtained as follow:

Anticlockwise moment = clockwise moment

Anticlockwise moment = 50 x 20

Clockwise moment = M x 30

Anticlockwise moment = clockwise moment

50 x 20 = M x 30

Divide both side by 30

M = (50 x 20)/30

M = 33.3 g ≈ 33 g

Therefore, the mass that will balanced the plank at the 70 cm length is appropriately 33 g

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