A-LevelPhysicsPhysical quantities and units9702/22 · May/June 2020 · Q16 Marks
Define velocity.
- (a)Define velocity.[1]
- (b)The drag force FƉ acting on a car moving with speed v along a straight horizontal road is given by FD = v²Ak where k is a constant and A is the cross-sectional area of the car. Determine the SI base units of k.[2]
- (c)The value of k, in SI base units, for the car in (b) is 0.24. The cross-sectional area A of the car is 5.1 m². The car is travelling with a constant speed along a straight road and the output power of the engine is 4.8 x 10⁴ W. Assume that the output power of the engine is equal to the rate at which the drag force FƉ is doing work against the car. Determine the speed of the car.[3]
Mark scheme
Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.
- [1] (velocity =) change in displacement/ time (taken)
- [C1] units of F: kg m s-2
- [A1] units of k: kg m s-2/ [m² × (m s-1)2] = kg m-3
- [C1] P = Fv
- [C1] 4.8 x 104 = 0.24 × 5.1 × v3
- [A1] v = 34 m s-1
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