A problem about spring constant

[katie7la]

A plane weighing 220 kN (25 tons) lands on an aircraft carrier. The plane is moving horizontally at 64.0 m/s (141 mi/h) when its tailhook grabs hold of the arresting cables. The cables bring the plane to a stop in a distance of 84.0 m.
(a) How much work is done on the plane by the arresting cables?
(b) What is the force (assumed constant) exerted on the plane by the cables?

(a)
For this problem I used
Work = K where K =1/2(mv^2)
k=1/2((220)(64^2))
k = 450.56

(b) work = F*x
450.56 = F*84
F=5.36


However, I got it wrong. What am I doing wrong?

 

[Doc Al]

(a)
For this problem I used
Work = K where K =1/2(mv^2)
k=1/2((220)(64^2))
k = 450.56

What's the mass of the plane? Redo this calculation, taking care with units.

(b) work = F*x
450.56 = F*84
F=5.36

Your method is OK, but your answer from part a is way, way off. (Realize that a force of 5.36 Newtons is about a pound of force--way too low to be realistic.)

 

[kbyws37]

Sorry, but I'm still having trouble. The plane weighs 220kN (25 tons).
So should i convert the tons into kilograms? 1 ton = 1000kg so it would be 25000 kilograms??
and then from there on do i use the equation...
Work = K where K =1/2(mv^2)

 

[Doc Al]

Why do you have two different IDs?

The plane weighs 220kN (25 tons).
So should i convert the tons into kilograms? 1 ton = 1000kg so it would be 25000 kilograms??

That's a metric ton; instead, convert Newton's to kg via: weight = mg.

and then from there on do i use the equation...
Work = K where K =1/2(mv^2)

Yes.