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mangaman81
Lv 5
mangaman81 asked in Science & MathematicsPhysics · 8 years ago

Physics Angular Momentum Vector Question?

Hiya!

This question reads:

A particle of mass 0.40 kg is moving with velocity v = (5.0i + 6.0j) m/s.

(a) Find the angular momentum L relative to the origin when the particle is at r = (2.0j + 3.0k) m.

I'm meant to answer in terms of i, j, and k.

My understanding is that L = v * r * m

So that would give me m * (v x r), so I do the cross product:

[5 6 0]

[0 2 3]

I tried to find i, which would be 6 * 3 - 0 * 2 = 18 * .4 = 7.2, however this is not correct.

What am I doing wrong?

Thanks!

1 Answer

Relevance
  • ?
    Lv 6
    8 years ago
    Favourite answer

    L = (r x p) = m*( r x v)

    Note: You got the order backwards, its r x v, and not v x r.

    [i j k]

    [0 2 3]

    [5 6 0]

    Lx = .4 ( 2*0 - 3*6) = -7.2 kg m^2/s

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