Answer:
The acceleration would be positive, pointing to the right.
Explanation:
The acceleration tells us how velocity changes every second. If the train stops, this means its velocity must go from a non-zero value to zero.
To reduce velocity, acceleration must point to the opposite direction. Since velocity is negative, acceleration must be positive.
Since both start with the same vertical velocity from the same position with the same acceleration they will reach the lake at the same time.
