Last year I had been on a business trip to China. I had heard a lot about Maglev Trains and I was looking forward to train which can run at 540 km/hr. the physicist in me compelled me to cary a home made accelerometer with me. It was a simple bob hanging from a support. as train would accelerate, the bob would be pushed backwards by pseudo force. its angular position would tell me the acceleration. i had my laptop hooked onto is so that it could plot a graph of `tan theta` against time. i could look at the beutiful scenery outside rather than botering about the accerometer. the accelerometer was oriented length wise so that it could only measure acceleration or decleration along the velocity of the train.

Many of times the train took sharp turns. the journey lasted for an hour. after my return, I opened my laptop and cheaked out the graph. the graph reas as follows.

What is the value of `tan theta` during last 20 minuts of the journeys ?