O-LevelPhysicsKinematics5054/22 · May/June 2014 · Q915 Marks

A children's ride consists of a steel cable that runs between two posts of different heights, as shown in Fig. 9.1. A girl starts and finishes the ride at rest. Her horizontal motion can be taken as • an initial uniform acceleration for 3.0s, followed by • a constant speed of 2.4m/s for a further 5.0s and • a final uniform deceleration that lasts for 1.0s. [Figure 9.1]

(a)On Fig. 9.2, draw a speed-time graph of the horizontal motion. [Figure 9.2][3]
(b)Explain what is meant by uniform acceleration.[2]
(c)The final deceleration is larger in size than the initial acceleration. Explain how the data shows this.[1]
(d)Calculate the horizontal distance travelled by the girl in the first 8.0s.[3]
(e)(i)The girl has a mass of 30kg and falls a vertical distance of 1.6m during the ride. The gravitational field strength g is 10N/kg. Calculate the decrease in gravitational potential energy of the girl.[2]
(e)(ii)The gain in kinetic energy of the girl is less than the decrease in her potential energy. Suggest one reason for this.[1]
(f)A group of pupils make measurements to show that the girl's speed is constant during the middle section of the ride. Suggest what measurements are made and how they show that the speed is constant.[3]

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Mark scheme

Marking points from the official mark scheme (May/June 2014). The mark or mark type is shown in brackets.

[B1] (a) straight line from (0, 0) to (3, 2.4)
[B1] horizontal line from 3s to 8 s
[B1] straight line from end of a horizontal line to zero in 1s
[C1] (b) constant/same increase in velocity or constant change in velocity
[A1] constant/same increase in velocity per sec/unit time
[B1] (c) occurs in a short(er) time
or acceleration took 3 s and deceleration took 1 s
[C1] (d) (d =) speed × time numerical or algebraic or area under graph clear
[C1] 1.2 x 3 or 3.6 (m) or 2.4 × 5 or 12 seen
[A1] 15.6 m or 16 m
[C1] (e) (i) mgh seen in any algebraic or numerical form, e.g. 30 × 10 × 1.6
[A1] 480 J
[B1] (ii) heat or thermal energy or sound produced
or work done against friction/air resistance
[C1] (f) at least two distances and corresponding times mentioned
[A1] how the actual measurement is made, e.g. (any one from) • make mark on ground every second and measure distances • note video position every sec and use a scale to find distances • make mark on ground every meter and measure/take time as girl passes
[B1] how constant speed is proved using measurement, e.g. (any one from) • same distance between each position for the same time interval • same time interval for equal distances • Δd/Δt constant or slope of distance-time graph constant

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