Final answer:
The velocity at 2.9 seconds depends on the initial speed at 2 seconds and the subsequent forces acting on the person. However, without the mass, we cannot calculate the new speed at 2.9 seconds; only her last known speed at 2 seconds is available.
Step-by-step explanation:
To calculate her velocity at 2.9 seconds, we must consider her initial speed and the forces acting on her after 2 seconds. Given her initial speed of 19.6 m/s at 2 seconds and a force of 76 N upward for the duration of 2 to 10 seconds, we can find her acceleration using Newton's second law (Force = mass x acceleration), where Force = 76 N and mass (m) is not provided. If we had the mass, we could calculate the acceleration (a) and use the equation V = V0 + at to find the velocity at 2.9 seconds. Without the mass of the parachutist, we cannot calculate the acceleration or update the velocity. We only know that, unless acted upon by another force, the parachutist had a speed of 19.6 m/s at 2s which is the last known velocity without further information.