O-LevelPhysicsForces5054/22 · May/June 2023 · Q18 Marks

Fig. 1.1 shows the speed-time graph for a car travelling on a straight horizontal road. [Figure 1.1]

(a)Describe the motion of the car shown in Fig. 1.1.[2]
(b)(i)At time t = 10 s the engine of the car is switched off. The brakes are not applied. Name two forces that act on the car to cause the change in motion after t = 10s. 1 2[1]
(b)(ii)Suggest why Fig. 1.1 is a curve after t = 10s.[1]
(c)(i)Between t = 10s and t = 20s the speed of the car changes from 18m/s to 11 m/s. The mass of the car is 1200 kg. Calculate the change in momentum of the car in this time. Give the unit of your answer momentum change = ................................................. unit .........[2]
(c)(ii)Calculate the average resultant force exerted on the car during this time. average resultant force = ................................................. N[2]

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Mark scheme

Marking points from the official mark scheme (May/June 2023). The mark or mark type is shown in brackets.

[B1] speed is constant for 10 s / at first
[B1] deceleration
[B1] friction (with road) and air resistance or (air) drag
[B1] resistive force(s) change / decrease (as speed decreases) or (graph shows) deceleration is not constant / decreases or non-uniform decrease in speed
[C1] (momentum =) mv in any form algebraic or numerical
[A1] 8400 and kg m/s or Ns
[C1] (F =) Δmv / t or F = ma in any form algebraic or numerical
[A1] 840 (N)

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