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**1. The problem statement, all variables and given/known data**

A 2.0 kg block is initially at rest on the positive x-axis 2.0 m from the origin. It is acted on by a constant force F = (4.0i − 4.0 j)N. After this force has acted for 3 s, what is the angular momentum of the block (in kg.m2/s) about the origin?

**2. Relevant equations**

F=ma

x = (x0) + (v0)t + (1/2)at^2

v = v0 +axt

L=rXP

**3. The attempt at a solution**

Fx=m(ax) = 2 m/s^2

Fy=m(ay) = -2 m/s^2

(Vx0)=0 (Vx)=0+2(3)=6 m/s

(Vy0)=0 (Vy)=0+(-2)(3)=-6 m/s

so, V= 6i-6j m/s

(rx)=2+1/2(2)(3)^2

=11

(ry)=0+1/2(-2)(3)^2

=-9

so, r= 11i-9 m

L= rXP = rXmV= (11i-6j)X(2)(6i-6j)

= (11i-6j)X(12i-12j)

= (-66k-56k)

=-112k m^2/s

The correct answer is -24k.

I am not sure what I have done wrong.

This is for studying for an exam I have on Saturday.

Thanks,

Ray