Calculating Impulse and Force: Understanding the Concept Behind It

[Ignitia]

This is in relation to a homework question: But I don't need assistance on the question itself, but the concept behind it.

A mass of .4kg travels in the positive direction for 67m/s until a separate force is applied to M in the negative direction at 14m/s for .027 seconds. Impulse = 32.4 It then asks, "What is the average magnitude of the force?"

I'm more confused on the wording - as to what is it asking specifically? Why is the force being asked to be represented as a magnitude when it should have direction as well?

J = F Δt
F=J/Δt
F= -32.4N*s/.027s
F=-1200N

Yet the answer states 1200N. Impulse should be negative, since it's coming in from the negative direction, right?

What am I missing?

 

[person123]

It asks for the magnitude of the force, so therefore it would always be positive.

You also seem to be confusing impulse and impact; the former is the change in momentum not the force applied.

 

[Dale]

It probably should have been worded "magnitude of the average force"

 

[Ignitia]

You also seem to be confusing impulse and impact; the former is the change in momentum not the force applied.

I don't follow. I calculated the change of time in there: J=FΔt.

It probably should have been worded "magnitude of the average force"

That makes more sense. I realized I calculated directions into it when it didn't ask for it.

 

[person123]

1200 Newtons is not the impulse; I'm not sure whether you thought it was or not.

 

[Ignitia]

1200 Newtons is not the impulse; I'm not sure whether you thought it was or not.

No no. Impulse was 32.4N*s in the negative direction. 1200N is the force.

 

[person123]

Oh, okay. It all seems good.

 

[Arjan82]

Well, force consists of both a magnitude and a direction. You were already given the direction (the negative direction) so the only thing that's left to determine is the magnitude :).