When a train first starts going down the railroad, it is very difficult for it to get going. When it comes to a stop, it has a hard time slowing down. Why is this?

A: balanced forces
B: unbalanced forces
C: inertia

Explanation:

When we apply the force on any body , the inertia comes into play . It is the tenancy of the the body to oppose the force which tends to change its state .

In first case the train tries to change its state from rest to motion . Thus the inertia of rest opposes this tendency.

In the second case , the train tries to come from motion to the state of rest . Thus again , inertia opposes it .

Therefore inertia is the factor which creates difficulty in both case . Hence option ( c ) is correct  

it takes about 30 days for it to break down