The trains take <u>57.4 s</u> to pass each other.
Two trains A and B move towards each other. Let A move along the positive x axis and B along the negative x axis.
therefore,

The relative velocity of the train A with respect to B is given by,

If the train B is assumed to be at rest, the train A would appear to move towards it with a speed of 170 km/h.
The trains are a distance d = 2.71 km apart.
Since speed is the distance traveled per unit time, the time taken by the trains to cross each other is given by,

Substitute 2.71 km for d and 170 km/h for 

Express the time in seconds.

Thus, the trains cross each other in <u>57.4 s</u>.
Answer:
a cold air mass and a warm air mass merge together
Answer:
d) Wind
Explanation:
Secondary energy is energy produced by converting energy available in its natural state in the environment. Hence Wind is a primary source not a secondary source
If its atomic number is 48, then it has 48 protons in the nucleus
of each atom. Any more mass than that is supplied by the neutrons
that are mixed in there with the protons.
If the mass is 167, and 48 of those are protons, then there are
(167 - 48) = 119 neutrons
in each nucleus.