O-LevelPhysicsForces5054/22 · May/June 2021 · Q36 Marks

Fig. 3.1 shows a small brick hanging from a newton meter. [Figure 3.1] The reading on the newton meter is 3.0N.

(a)Describe how the reading on the newton meter is used to find the mass of the brick.[1]
(b)(i)State the principle of moments for a body in equilibrium.[1]
(b)(ii)Determine the reading on the newton meter shown in Fig. 3.2. reading =[2]
(c)A beaker of water is placed so that the brick is partly submerged in the water, as shown in Fig. 3.3. The apparatus is adjusted to keep the rule horizontal. [Figure 3.3] Suggest why the reading on the newton meter is less than your answer in (b)(ii).[2]

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Mark scheme

Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.

[B1] (mass = ) meter reading / g meter reading / gravitational field (strength meter reading / acceleration due to gravity
[B1] (sum of) clockwise moments = (sum of) anticlockwise moments (about any point)
[C1] any attempt at using moments, e.g. 3 × 30 = F × 20
[A1] 4.5 N
[B1] force upwards (on brick due to water) or force due to water (on brick) or force downwards (on brick) is reduced / counteracted (by water) or force exerted by brick (on rule) reduced or force / tension in string reduced
[B1] (force caused by) pressure (of water) or reduced anticlockwise moment

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