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In the javelin throw at a track-and-field event, the javelin is launched at a speed of 29 m/s at an angle of

36^\circ
36
∘


above the horizontal. As the javelin travel s upward, its velocity points above the horizontal at an angle that decreases as time passes. How much time is required for the angle to be reduced from

36^\circ
36
∘


at launch to

18^\circ?
18
∘
?