A mass of 4 kg originally at rest is pulled by a string along a smooth horizontal surface. The force of 15 N is maintained until the mass undergoes a displacement of 20m. at which stage the mass is allowed to keep moving at constant velocity.
What would be the velocity of the mass at the end of 20 m ?

Explanation

To find the velocity of the mass at the end of 20 meters, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Given Values**:
- Mass (m) = 4 kg
- Force (F) = 15 N
- Displacement (s) = 20 m
...