O-LevelPhysicsKinematics5054/22 · Oct/Nov 2014 · Q915 Marks

Explain what is meant by uniform acceleration.

(a)Explain what is meant by uniform acceleration.[2]
(b)Acceleration is a vector quantity. State how a vector quantity differs from a scalar quantity.[1]
(c)A rock from space is travelling in a straight line at high speed when it enters the Earth's atmosphere. Fig. 9.1 is the speed-time graph for the rock from time t = 0 to time t = 50s. [Figure 9.1]
(c)(i)On Fig. 9.1, mark • a letter X, where the rock is moving with a constant speed, • a letter Y, where the rock has a uniform deceleration, • a letter Z, where the rock has a non-uniform deceleration.[3]
(c)(ii)1.At time t = 25s, the mass of the rock is 8.4 kg. For the time t = 25s, determine the size of the acceleration of the rock,[3]
(c)(ii)2.the size of the resultant force on the rock.[2]
(c)(iii)1.Fig. 9.2 shows the rock at t = 25 s. [Figure 9.2 (not to scale)] On Fig. 9.2, draw and label two arrows to show the directions of the gravitational force F and the air resistance R acting on the rock.[2]
(c)(iii)2.Suggest why the size of the air resistance changes as the rock travels through the Earth's atmosphere.[1]
(c)(iv)Suggest what happens to the rock at t = 40s.[1]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

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

[1] changing speed/velocity
[1] change in speed/velocity/time constant or (v-u)/t constant or constant/equal rate of change of speed/velocity
[1] (a vector quantity has) direction
[1] 1. X between t ≥ 0 and t < 10 s
[1] 2. Y between t > 20s and t < 30 s
[1] 3. Z between t > 10s and t < 20 s or between t > 30s and t < 40 s
[1] two speed values from graph between 15 and 35s (±1mm)
[1] two corresponding time values from graph between 15 and 35 s (±1 mm) or (a = )Av/t
[1] 500 m/s²
[1] (F = ) ma or 8.4 × 500
[1] 4200 N
[1] arrow labelled F perpendicular to surface of Earth
[1] arrow labelled R opposite to direction of travel (by eye) from rock
[1] speed changes or density/pressure of air changes or cross-sectional area (of rock) changes
[1] it hits the ground/surface of the earth or stops or speed is zero

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