O-LevelPhysicsForces5054/22 · May/June 2015 · Q27 Marks
Fig. 2.1 shows two engineers measuring the length of a wall made from concrete. [Figure 2.1 (not to scale)] The wall is 2.0m high, 15m long and 0.25 m thick. The weight of the wall is 180000N and the mass of the wall is 18000 kg.
- (a)The engineers measure the length of the wall in one single measurement. State the name of the measuring instrument they use.[1]
- (b)(i)Define density.[1]
- (b)(ii)Calculate the density of the concrete. density =[2]
- (b)(iii)Calculate the pressure exerted by the wall on the ground. pressure =[2]
- (b)(iv)Without further calculation, explain why doubling the length of the wall does not change the pressure that the wall exerts on the ground.[1]
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Mark scheme
Marking points from the official mark scheme (May/June 2015). The mark or mark type is shown in brackets.
- [1] (a) tape
- [1] (b) (i) mass ÷ volume or mass per unit volume
- [1] (b) (ii) (V=) 15 × 0.25 × 2 or 7.5 seen
- [1] (b) (ii) 2400 kg/m³
- [1] (b) (iii) (A=) 15 × 0.25 or 3.75 or (P=) F/A
- or (P=) 180000/A or (P=) dgh / pgh seen
- [1] (b) (iii) 48 000 Pa
- [1] (b) (iv) (length doubles) so both area and weight/force double
- or area and force/weight both increase/larger (in proportion)
- or height and density the same (in P = dgh)
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