Ok I need some guidance with the second part of this problem. I attached two graphs hastily constructed with paint and which are somewhat lopsided, so keep in mind that they are by no means correct geometrically.
A train travels from a station P to the next station Q, arriving at Q exactly 5 minutes after leaving P. The (t,v) graph for the trainís journey is approximated by three straight line segments as shown in figure 1.
Write down the acceleration of the train during the first minute of the journey (I found 0.5 ms^-2 which is correct)
Find the distance from P to Q (I found 7200m which is correct)
On one occasion when the track is being repaired, the train is restricted to a maximum speed of 10ms^-1 for the 2000m of track lying midway between P and Q. The train always accelerates and decelerates at the rate shown in figure 1. When not accelerating or decelerating or moving at the restricted speed of 10ms^-1, the train travels at 30ms^-1. Sketch the (t,v) graph for the journey from P to Q when the speed restriction is in force, and hence find how long the train takes to travel from P to Q on this occasion.
I sketched figure 2 for this part. A=E=0.5x60x30=900m, C=2000m
So B=D=(7200 Ė 1800 -2000)/2 = 1700
From this I calculate the time taken over B: 1700= 0.5 (10 + 30) t and get t= 85s
85x2 + 200 + 60 x 2 = 490s
But this is wrong, Iím supposed to get 460! What is wrong?