Physics

Problem

A train must travel

1.2\,\text{km}

between two stations. It starts from rest, accelerates uniformly at

1\,\text{m}\,\text{s}^{-2}

until it reaches

20\,\text{m}\,\text{s}^{-1}

, runs at this speed for some time, and finally decelerates uniformly at

2\,\text{m}\,\text{s}^{-2}

to come to rest at the next station. The minimum possible time for the journey is closest to a)

70\,\text{s}

60\,\text{s}

75\,\text{s}

85\,\text{s}