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June 9th, 2012, 11:30 AM   #1
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A train of 3000 KN

Hi all

1 ) A train of 3000 KN weight starts from rest and reached a velocity of 54 km/h after one min . if the frictional resistance of the track is 5N/KN of the train's weight . Find the tractive force developed by the engine ?

I don't understand what is mean "tractive force " ??

[color=#FF0000]anyway I start solve the question

w = 3000 kN
mass = 305810
u = 0
v = 54 km/h

v = u + at
a = 0.25
F = m X a
F = 305810 X 0.25
76452.5 N
[/color]

2 ) A parachute weighing 500 N falling with uniform acceleration from rest, descends 5 m in the first 4s. Find the resultant of air on the parachute .
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June 9th, 2012, 12:44 PM   #2
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Re: A train of 3000 KN

1.)

We need to find the final velocity in meters per second:



Hence:



Your answer is correct.

2.) First, we may find the net force on the parachute:



Now, if we let be the resultant force of air on the parachute, we have:



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June 10th, 2012, 06:31 AM   #3
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Re: A train of 3000 KN

teacher said the answer for first one is not complete

he said

F = p - ( 5 X 3000 )
F = p - 15000 kN

I don't know what he mean ?
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June 10th, 2012, 08:21 AM   #4
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Re: A train of 3000 KN

It appears that he means you need to add the resistive force to the result to get the total.
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June 10th, 2012, 08:37 AM   #5
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Re: A train of 3000 KN

Are you mean tractive force = force + resistive force or what ?

and I want know ,,, what is the difference between force which arr got and tractive force ?
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June 10th, 2012, 11:21 AM   #6
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Re: A train of 3000 KN

For Q 2 ...

Fnet = m Xa

(500/9.81 ) X ( 0.625 ) = 31.85 N

I don't know How you got ( 0.14 N )
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June 10th, 2012, 11:30 AM   #7
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Re: A train of 3000 KN

How did you get 0.625 for the acceleration?

I get 1/360 using which comes from where .
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June 10th, 2012, 11:40 AM   #8
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Re: A train of 3000 KN

see

h = ut+1/2at^2
5 = 0 + 0.5a(4^)2
a = 5/8 which is 0.625 ?? where is the mistake ?
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June 10th, 2012, 11:58 AM   #9
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Re: A train of 3000 KN

Ooops, I used the time from the first problem.

Carry on...
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June 10th, 2012, 12:05 PM   #10
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Re: A train of 3000 KN

now I know all the answer just this formula
I don't know

why you said


F net = w - Fr

can please explain to me fully
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