Question

The two enda of a train moving with constant acceleration pass a certain point with velocities u and 3u. the velocity with which thw middle point of the train passes the same point is

Answer 1

l=length of train.
2al=9u^2-u^2=8u^2
a*l=4u^2

then
2a*l/2=v^2-u^2
a*l+u^2=v^2
5u^2=v^2
then v=u*root(5)