A small 0.300kg bird is flying horizontally at 3.50m/s toward a 0.750kg thin bar

Question

A small 0.300kg bird is flying horizontally at 3.50m/s toward a 0.750kg thin bar hnging vertically from a hook at its upper end, as shown in Figure 10.51. (a) When the bird is far from the bar, what are the magnitude and direction (clockwise or counterclockwise) of its angular momentum about a horizontal axis perpendicular to the plane of the figure and passing through (i) point A, (ii) point B, and (iii) point C? (b) Repeat part (a) when the bird is just ready to hit the bar, but is still flying horizontally.

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Explanation / Answer

A) (i)The angular momentum is the linear momentum times the normal (perpendicular) distance to the line of motion: Linear momentum = 0.300*3.50; the distance to A = 1.50 m; angular momentum =mvr= 1.58 kg*m²/s; the direction is counterclockwise

(ii) The linear momentum is the same, but the normal distance to point B is zero, so the angular momentum is zero

(iii) The linear momentum is the same, but the distance to C is 1.60 - 1.50 = 0.30 m; so the angular momentum is 0.315 kg*m²/s; The direction is clockwise

B) The answer will remain unchanged as the distance taken is the perpendicular distance between the given axis and the axis of flight of bird.

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