Answer:
1 second
Step-by-step explanation:
Assuming that the force is in the same direction as speed we can do the graphic.
- Draw the forces present on the problem (weight and the net force).
- Newton's second law. The summation of the forces is equal to the product between mass and aceleration.

- Plan the equation on x direction (because the mass is moving on that way). The result would be:

- From that equation we know that the aceleration is 5m/s2.
- Also, we know (because it is a uniform line movement) that the aceleration is related with the speed.
- Clearing the equation:

- And replacing:

- So, the force is applied for 1 second.