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Airplane on the runway 
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#1
Sep1507, 01:28 PM

P: 3

1. The problem statement, all variables and given/known data
A plane accelerates from rest at a constant rate of 5.00 m/s^2 along a runway that is 1800 m long. Assume that the plane reaches the required takeoff velocity at the end of the runway. What is the time t_{TO} needed to take off? 2. Relevant equations i think the formula i'm supposed to use is d = vt + 1/2at 3. The attempt at a solution not exactly sure if this is the correct formula but thats what i thought i have to use. we know that d = 1800m and we know that initial velocity = 0 and a = 5 m/s^2 so then we isolate for t. thus we get t = 1800 / 2.5 = 720. however i think this might be wrong because i don't think its realistic for a plane to take 12 minutes on the run way to take off. any ideas? Also part of the question was What is the distance d_last traveled by the plane in the last second before taking off? I tried to use the same formula d = vt + 1/2at and since we figured out time from part a we sub (t  1) into here and get distance traveled in the last second before taking off. not sure if any of this is right. can someone verify? Thank you 


#2
Sep1507, 01:31 PM

HW Helper
P: 4,124

your equation is wrong. it should be:
d = v0*t + (1/2)at^2 you didn't have the t^2... pluggin in t1... gives the distance travelled in the first t1 seconds... not the last 1 second. you're close... 


#3
Sep1507, 03:45 PM

P: 3

oops ya i forgot the square. so then i get 26.8 seconds. does that make sense for a plane to take amount of time for lift of? i think it makes sense to me. not sure. also does this mean that we don't care about the required velocity for takeoff?
hmmm the second part is tricky. i thoght that t  1 would mean that lets say it took 10 seconds then t = 10 and the second before it is t  1 = 9. i'm a bit confused on this part. 


#4
Sep1507, 03:47 PM

HW Helper
P: 4,124

Airplane on the runway
Suppose you know the distance travelled in the first 10 seconds... and the distance travelled in the first 9 seconds... you can get the distance in the last second by subtracting the two... 


#5
Sep1507, 03:54 PM

P: 3

Wow thanks for the fast reply. And thank you very much for all your help. i got both answers correct thanks to you. :)



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