A really confusing question on potential energy,

[i_hate_math]

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.

 

[drvrm]

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.

 

[CWatters]

Check where h0 is measured from.

 

[i_hate_math]

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

 

[i_hate_math]

Check where h0 is measured from.

Thanks!