The helicopter's net force at t = 5.0 seconds is F = 1.65 × 10⁴ i - 3.3 × 10³ k
Additional explanation
Newton's second law states that the acceleration caused by the net force acting on an object is directly proportional to that force and inversely proportional to the object's mass.

The sum of forces equals mass times acceleration (∑F = m·a).
Where F represents force (in Newtons), m is mass (in kilograms), and a is acceleration (in meters per second squared).
Velocity is the first derivative of position with respect to time:

Acceleration is the derivative of velocity with respect to time:

The position vector is given as r = 0.020 t³ i + 2.2 t j − 0.06 t² k.
Velocity (v) then is

v = 0.06 t² i + 2.2 j − 0.12 t k.
Acceleration (a) is

a = 0.12 t i − 0.12 k.
Also, weight (W) equals mass times gravity: W = m·g

The given force magnitude is 2.75 × 10⁵ N divided by g = 10 m/s², yielding
mass m = 2.75 × 10⁴ kg.
Therefore, net force is:
F = m × a = 2.75 × 10⁴ × (0.12 t i − 0.12 k)
At t = 5 s:
F = 2.75 × 10⁴ × (0.12 × 5 i − 0.12 k) = 2.75 × 10⁴ × (0.6 i − 0.12 k)
F = 1.65 × 10⁴ i − 3.3 × 10³ k