A Levels Physics

The graph shows how the total resistive force acting on a train varies with its speed.
Part of this force is due to wheel friction, which is constant. The rest is due to wind resistance.
40-
resistive force
/kN
30-
20-
10-
0+
50
100 150 200
speed /kmh-1
wind resistance
wheel friction
What is the ratio
at a speed of 200 km h-1?
A 4
в 5
C 8
D
10


Choice A is correct because:

The graph shows two components of resistive force acting on the train: wheel friction and wind resistance. At 200 km/h, the total resistive force is 40 kN.

The wheel friction is constant and appears to be 8 kN irrespective of the speed. Therefore, the wind resistance at 200 km/h is the total resistive force minus the wheel friction, which is 40 kN - 8 kN = 32kN.

The question asks for the ratio of the wind resistance to wheel friction. This is .

Choice B is incorrect because:

Choice B suggests a ratio of 5, which would imply that the wheel friction is 5 times the wind resistance. This is not consistent with the information given in the graph.

Choice C is incorrect because:

Choice C suggests a ratio of 8, which would imply that the wheel friction is 8 times the wind resistance. This is not consistent with the information given in the graph.

Choice D is incorrect because:

Choice D suggests a ratio of 10, which would imply that the wheel friction is 10 times the wind resistance. This is not consistent with the information given in the graph.

Terminal Velocity | 2013 - O/N - 9702/13 | Q16