D = 8cm H=8cm - Gauthmath

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Question

Fig. 2.1 shows a uniform metre rule PQ in equilibrium.  The distance PQ is 100 cm. The mass of the me  (i) On Fig 2.1, draw and label:  1. an arrow to show the force Wacting on PQ at the centre of mass  2. an arrow to show the force R acting on PQ at the pivot.  (ii) By taking moments about the pivot, calculate F.SHOW LESS0

Solution

F = 0.96N.

Explanation: (i)

  1. The force W acts downwards at the centre of mass of the metre rule, which is at the 50cm mark.
  2. The force R acts upwards at the pivot point.

(ii) Step 1: The metre rule is in equilibrium, so the sum of the clockwise moments about the pivot is equal to the sum of the anticlockwise moments about the pivot. Step 2: Clockwise moment = W x 40cm. Step 3: Anticlockwise moment = F x 50cm. Step 4: W x 40cm = F x 50cm. Step 5: W = 0.12kg x 10N/kg = 1.2N. Step 6: 1.2N x 40cm = F x 50cm. Step 7: F = (1.2N x 40cm)/50cm = 0.96N.

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