What is the spring constant of spring?

AI Thread Summary
The discussion revolves around calculating the spring constant for a scenario where a 60 kg person drops onto a spring-supported platform. The initial calculation used only the height of 1.20 m, but it was clarified that the total drop includes an additional 0.06 m due to the spring's compression. The correct formula to use is derived from energy conservation, equating gravitational potential energy to spring potential energy. The final calculation should incorporate the total drop of 1.26 m, leading to a revised spring constant of approximately 4.12 x 10^5 N/m. Understanding the total distance fallen is crucial for accurate results in such physics problems.
Mdhiggenz
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Homework Statement


A 60 kg person drops from rest a distance of 1.20 m to a platform of negligible mass supported by a stiff spring. The platform drops 6 cm before the person comes to rest. What is the spring constant of spring?


Homework Equations





The Attempt at a Solution



w=1/2kx^2

mgh=1/2kx^2

2(mgh)/x^2=k

2(60kg*9.8*1.20)/0.06m=3.92*10^5

the answer however is 4.12*10^5


What am I doing wrong?

Thank you
 
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The mass falls further than 1.20 as the spring compresses.
 
So would I add the 0.06m? Iam a bit confused
 
Correct. :smile:

The question says …
Mdhiggenz said:
A 60 kg person drops from rest a distance of 1.20 m to a platform

… after that it drops a further 0.06 m, so the total drop (for the person) is 1.26 m :wink:
 
Thx Tim
 
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
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