Physic-Conservation of momentu

2008-12-24 3:02 pm

A big bird of mass 2 kg dives down to catch a bat of mass 0.5kg. At the impact , the bird is traveling at a speed of 16m/s with an angle 60 deg. to the horizontal and the bat is traveling horizontally at 5m/s. Assuming the bird dives with wings folded and does not open them until it has caught the bat, at what angle to the horizontal does the bird move immediately after the impact? (hints: conservation of momentum)

回答 (1)

Audrey Hepburn

2008-12-24 4:05 pm

✔ 最佳答案

The velocity of the bird can be ressolved into two perpendicular components, namely the vertical and the horizontal components.

In both directions, momentum is conserved since there is no external force acting on the system (The bird and the bat).

By the law of conservation of momentum,

Vertically, Mua = (M + m)va

(2)(16sin60*) = (2 + 0.5)va

Final vertical velocity, va = 11.09 ms-1 (Downward)

Horizontally, Mua + mub = (M + m)v

(2)(16cos60*) + (0.5)(5) = (2 + 0.5)v

Final horizontal velocity, v = 7.4 ms-1

Let x be the required angle,

tanx = va / v

x = tan-1 (11.09 / 7.4)

x = 56.3*

Therefore, immediately after the impact, the bird moves in a direction making 56.3* with the horizontal. The bird is diving.

參考: Myself~~~

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