Question

The position of a 2.75

Answer 1

Newton's second law :

In order to find the net force, you need the mass and the acceleration.

Instead of the mass, they give you the weight of the helicopter:

Weight is the force of gravity:

So you can solve for the mass:

Next step is to find the acceleration. Acceleration is the second derivative of the position:

To find the derivative of a vector, you just have to find the derivative of each component.

First derivative of the position:

(note: something went wrong when uploading the question, I don't see the sign for the last component of the position, I see ?(0.060m/s2)t2k , I'm not sure if it's + or - , I'll assume it? a plus sign, if it's not, then everything else remains the same except changing that sign)

Now the second derivative:

So the acceleration is:

They ask for the force at t=5.0 seconds, so you need the acceleration at that instant. Replacing t with 5.0s :

(The units change to m/s2, because you are multiplying (m/s3) times (s). )

Now you can find the net force:

Distributing the mass multiplying each component of the acceleration, you get (kg)(m/s2) which is N .

Rounding using two significant figures, the answer is: