If a subway train is moving to the left (has a negative velocity) and then comes to a stop, what is the direction of its acceleration? is the acceleration positive or negative?

Negative acceleration

Explanation:

We know that

v= u+at

Where v is the final velocity

u is the initial velocity velocity

a is the acceleration

t is time

When final velocity of train will be zero .

v=0

0= u+at

a=- u/t

So from above we can say that acceleration will be negative .When acceleration is positive then train will never come in rest position.