Angular momentum using unit-vector notation

[maxalador]

Homework Statement

At one instant, force F: 4.0j N acts on a 0.25 kg object that has position^vector^V : (2.0t - 2.0k) m and velocity vector /: (-5.0i + 5.0k) m/s. About the origin and in unit- vector notation, what are (a) the object's angular momentum and (b)the torque acting on the object

m = .25kg
f = (4.0 N)j
v = (-5i + 5k)

Homework Equations

Torque = (Yz-Zy)+(Zx-Xz)+(Xy-Yx)
KE= 1/2mv^2 + 1/2lw^2

The Attempt at a Solution

A) not quite sure where to start with A

B) (2i + 4j -2k)*(-5i + 4j +5k)
((4*-2)-(5*4)) - ((-2*5)-(-5*-4))-((2*4)-(4*2))

 

[jackarms]

Just remember that angular momentum is given by:$$\stackrel{\rightarrow}{l} = \stackrel{\rightarrow}{r} \times \stackrel{\rightarrow}{p}$$ So finding it just means doing another cross product.