A firefighting crew uses a water cannon that shoots water at 27.0 m/s at a fixed

Question

A firefighting crew uses a water cannon that shoots water at 27.0 m/s at a fixed angle of 53.0 above the horizontal. The firefighters want to direct the water at a blaze that is 15.0 m above ground level.

Part A

How far from the building should they position their cannon? There are twopossibilities (d1<d2); can you get them both? (Hint: Start with a sketch showing the trajectory of the water.)

A firefighting crew uses a water cannon that shoots water at 27.0 m/s at a fixed angle of 53.0 above the horizontal. The firefighters want to direct the water at a blaze that is 15.0 m above ground level.

Part A

How far from the building should they position their cannon? There are twopossibilities (d1<d2); can you get them both? (Hint: Start with a sketch showing the trajectory of the water.)

Explanation / Answer

We know that

H = ut + at^2/ 2

15 = 27sin53t - 9.8t^2/2

4.9t^2 - 21.56t + 15 = 0

solving this quadratic equation we get

t =3.533sec , 0.87 sec

d = 27cos53 x t   = 57.41 m   and 14.14 m

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