# Calculate Fnet to Find Change in Momentum

• physco827

#### physco827

[SOLVED] What is Fnet?

I am given a problem with an initial velocity then a final velocity, the weight and how long it took to change that velocity. They want us to get the change in momentum, but I don't know how to compute the Fnet to use in the equation. Any suggestions on the steps I should take?

To find the change in momentum, just calculate the final momentum and the initial momentum and find the difference. (Remember that momentum is a vector, so direction counts.)

What's the definition of momentum?

Thank you Doc Al for replying.

Momentum is p = (gamma)(mass)(velocity)

Having said that I still don't understand how to compute Fnet given two vectors, a mass, and a time.

I would just like to know how to compute the net force, Fnet, given the circumstances.

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Momentum is p = (gamma)(mass)(velocity)
Is this a question about relativistic dynamics? Or ordinary non-relativistic physics?

Having said that I still don't understand how to compute Fnet given two vectors, a mass, and a time.
Are you familiar with the impulse-momentum theorem? http://hyperphysics.phy-astr.gsu.edu/Hbase/impulse.html" [Broken]

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Actually I was not.

That link for impulse might help me out.

The force average is the mass(change in velocity)/(change in time).

The question is as follows:(took out number, substitiued x so you can't solve it for me so i can try to figure it out)
You were driving a car with velocity <x, x, x> m/s. You quickly turned and braked, and your velocity became <x, 0, x> m/s. The mass of the car was x kg. The maneuver took x seconds. What was the average net (vector) force acting on the car?

So to get that do i just use the force average formula?

Yes, that will work. Take care to find the change in velocity correctly (subtract them as vectors).

Thank you very much Doc.

I solved the equation thanks to your help and now know what Fnet is. You are awesome.