O-LevelPhysicsForces5054/22 · Oct/Nov 2017 · Q36 Marks

A solid, rectangular concrete block is lying horizontally on flat ground with one of its largest sides in contact with the ground. [Figure 3.1] shows the dimensions of the block. The weight of the block is 240 N.

(a)Calculate the pressure on the ground caused by the block.[2]
(b)State why the total pressure on the ground underneath the block is larger than the value obtained in (a).[1]
(c)(i)The block is of uniform density. State the height of the centre of mass of the block above the ground.[1]
(c)(ii)The block is rotated about its lower, left-hand edge so that it comes to rest on one of its smallest sides. This is shown in [Figure 3.2]. Explain why work is done as the block is rotated.[2]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2017). The mark or mark type is shown in brackets.

[C1] (P =) F/A or 240/(0.44 × 0.21) or 240/0.092(4)
[A1] 2.6 x 10³ Pa
[B1] atmospheric pressure (is acting on the block/ground)
[B1] 0.065 m or 6.5 cm or 65 mm
[B1] centre of mass rises
[B1] gravitational potential energy gained
or II
[B1] block has weight
[B1] force moves or something moves in direction of force or force makes block move/rotate

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