- #1
ojsimon
- 56
- 0
Hi,
I have just tried a momentum question involving springs. I got the wrong answer and the method used in the solution is different, but i still do not see what i did wrong.
The question is: a railway engine 6.2*10^4 and a carriage 4*10^4 have coupled. They have hit a buffer spring (to stop them) from an initial speed of 0.15m/s. Assuming the buffer behaves like a spring of stiffness 320kN/m calculate the maximum compressiion of the spring.
The solution given is:
Kinetic energy of train :
0.5 × 10.2 × 104 × 0.152 = 1150 J
0.5* F e
= 0.5× (k e) × e = 0.5 × k e^2
0.5 × 320 × 103 e2 = 1150 1
gives compression e = 8.47 × 10^-2 m
My Solution
F=Change in MV/Change in time F= Ke
so:
MV/T = Ke
s= ((u+v)/2)t Therefore : t=(40/3)e
so Mv= 40/3(Ke^2)
And i calculate e=0.059 m
But this is different to the solution given, why does my method not work?
Thanks
I have just tried a momentum question involving springs. I got the wrong answer and the method used in the solution is different, but i still do not see what i did wrong.
The question is: a railway engine 6.2*10^4 and a carriage 4*10^4 have coupled. They have hit a buffer spring (to stop them) from an initial speed of 0.15m/s. Assuming the buffer behaves like a spring of stiffness 320kN/m calculate the maximum compressiion of the spring.
The solution given is:
Kinetic energy of train :
0.5 × 10.2 × 104 × 0.152 = 1150 J
0.5* F e
= 0.5× (k e) × e = 0.5 × k e^2
0.5 × 320 × 103 e2 = 1150 1
gives compression e = 8.47 × 10^-2 m
My Solution
F=Change in MV/Change in time F= Ke
so:
MV/T = Ke
s= ((u+v)/2)t Therefore : t=(40/3)e
so Mv= 40/3(Ke^2)
And i calculate e=0.059 m
But this is different to the solution given, why does my method not work?
Thanks