A Boeing 747 ""Jumbo Jet"" has a length of 59.7 m. The runway on which the plane lands intersects another runway. The width of the intersection is 25.0 m. The plane decelerates through the intersection at a rate of 5.70 m/s2 and clears it with a fi nal speed of 45.0 m/s. How much time is needed for the plane to clear the intersection?

Question

Physics

Paris

17 May, 07:20

A Boeing 747 ""Jumbo Jet"" has a length of 59.7 m. The runway on which the plane lands intersects another runway. The width of the intersection is 25.0 m. The plane decelerates through the intersection at a rate of 5.70 m/s2 and clears it with a fi nal speed of 45.0 m/s. How much time is needed for the plane to clear the intersection?

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Red Hot · Answer 1

1.7 seconds

Explanation:

To clear the intersection, the total distance to be covered = 59.7 + 25 = 84.7m

first we need to find the initial speed to just enter the intersection by using the third equation of motion

v^2 - u^2 = 2*a*s

45^2 - u^2 = 2 * - 5.7 * 84.7

u^2 = 45^2 + 965.58

u^2 = 2990.58

u = 54.7 m/s

Now for time we apply the first equation of motion

v-u = a * t

t = (v-u) / a = (45 - 54.7) / -5.7 = 1.7seconds