A Boeing 747 "Jumbo Jet" has a length of 59.7m. The runway on which the plane lands intersects another runway. The width of the intersection is 25.0m. The plane decelerates through the intersection at a rate of 5.7 m/s(squared) and clears it with a final speed of 45.0 m/s. How much time is needed for the plane to clear the intersection?

3 answers

d(tot) = 25 + 59.7 = 84.7m.

Vf^2 = Vo^2 + 2*(-5.7)84.7 = (45)^2,
Vo^2 - 965.58 = 2025,
Vo^2 = 2025 + 965.58 = 2990.58,
Vo = 54.7m/s.

Vf = Vo + at,
Vf = 54.7 - 5.7t = 45,
54.7 - 5.7t = 45,
-5.7t = 45-54.7 = -9.7,
t = -9.7 / -5.7 = 1.70s.

1.7 seconds

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