ch11-p076 - 76 Both r and v lie in the xy plane The...

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in kg m 2 /s. This implies the particle is moving clockwise (as observed by someone on the + z axis) for t > 0. (b) The torque is caused by the (net) force G G Fm a = where 2 ˆ (1 2i )m / s. dv at dt == G G The remark above that only the y component of G r still applies, since a y = 0. We use G G G G G τ =× = × rFm ra bg and obtain () ( ) ( ) ˆˆ 2.0 2.0 12 k 48 k N m. tt =− = G The torque on the particle (as observed by someone on the + z axis) is clockwise, causing the particle motion (which was clockwise to begin with) to increase. (c) We replace G r with G r (measured relative to the new reference point) and note (again) that only its y component matters in these calculations. Thus, with y = –2.0 – (–3.0) = 1.0 m, we find ()() 22 2 2.0 1.0 6.0 k (12 k) kg m /s. =−− = G A . The fact that this is positive implies that the particle is moving counterclockwise relative to the new reference point. (d) Using G G G G G ′ = ×= ′ × rF m , we obtain ( ) 2.0 1.0
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