A really confusing question on potential energy,

Join the discussion
Registration is free. Ask a follow-up in this thread, or start your own.
Sign up Log in
4 replies · 2K views
i_hate_math
Messages
150
Reaction score
2

Homework Statement


A 975 g block is released from rest at height h0 above a vertical spring with spring constant k = 410 N/m and negligible mass. The block sticks to the spring and momentarily stops after compressing the spring 24.2 cm. How much work is done (a) by the block on the spring and (b) by the spring on the block? (c) What is the value of h0? (d) If the block were released from height 4h0 above the spring, what would be the maximum compression of the spring?

Homework Equations


Mechanical Energy: Emec=K+U
Conservation of Emec: K2+U2=K1+U1
Elastic Potential Energy: U(x)=0.5mk^2
Gravitational Potential Energy: U=mgh

The Attempt at a Solution


Part a&b are fairly straight forward I've got them right,
my attempt for part c was to set the "momentarily stop" as 0 for the height, and thus have
mgh0 = 0.5kx^2
and h0=1.256475144... but i was marked incorrect for this value.
so is my answer to part d, x=0.484m wrong.
 

Discussion

Physics news on Phys.org
i_hate_math said:

Homework Statement


A 975 g block is released from rest at height h0 above a vertical spring with spring constant k = 410 N/m and negligible mass. The block sticks to the spring and momentarily stops after compressing the spring 24.2 cm. How much work is done (a) by the block on the spring and (b) by the spring on the block? (c) What is the value of h0? (d) If the block were released from height 4h0 above the spring, what would be the maximum compression of the spring?

Homework Equations


Mechanical Energy: Emec=K+U
Conservation of Emec: K2+U2=K1+U1
Elastic Potential Energy: U(x)=0.5mk^2
Gravitational Potential Energy: U=mgh

The Attempt at a Solution


Part a&b are fairly straight forward I've got them right,
my attempt for part c was to set the "momentarily stop" as 0 for the height, and thus have
mgh0 = 0.5kx^2
and h0=1.256475144... but i was marked incorrect for this value.
so is my answer to part d, x=0.484m wrong.

i think you have missed a point in energy conservation - the change in P.E. =mg (ho+x) as the mass moves down during comprssion of the spring . so your energy gets missing by part mgx-ho should be less.
 
  • Like
Likes   Reactions: i_hate_math
drvrm said:
i think you have missed a point in energy conservation - the change in P.E. =mg (ho+x) as the mass moves down during comprssion of the spring . so your energy gets missing by part mgx-ho should be less.
Thanks a lot mate
 
CWatters said:
Check where h0 is measured from.
Thanks!