Spring kinetic energy problem

  • Thread starter Nicholson
  • Start date
  • #1
4
0
I think I understand how to begin the problem but when I compute the answers they don't match the selected answers in the back of the book

Homework Statement



A spring (k=200 N/m) is fixed at the top of a frictionless plane inclined at angle θ=40°. A 1/0 kg block is projected up the plane, from an initial position that is distance d=0.60m from the end of the relaxed spring, with an initial kinetic energy of 16 J.
a) What is the kinetic energy of the block at the instant it has compressed the spring 0.20 m?
b) With what kinetic energy must the block be projected up the plane if it is to stop momentarily when it has compressed the spring by 0.40m?

Homework Equations



Wf=ΔK+ΔU=Kf-Ki+Uf-Ui

The Attempt at a Solution



a) Ki is the 16 J of KE from the block, Ui is 1/2Kx^2 from the original compressed distance, Uf is 1/2Kx^2 at the instant the spring is compressed to 0.20m.

(Kf-16J) + [(1/2(200 N/m)(0.6)^2)-(1/2(200 N/m)(0.8)^2)]

Answer should be 7 J but I must be off somehow because thats not what I get
 
Last edited:

Answers and Replies

  • #2
Doc Al
Mentor
45,186
1,515
Don't forget gravitational PE.
 

Related Threads on Spring kinetic energy problem

Replies
1
Views
5K
Replies
1
Views
1K
Replies
2
Views
7K
  • Last Post
Replies
8
Views
1K
  • Last Post
Replies
8
Views
10K
  • Last Post
Replies
3
Views
1K
  • Last Post
Replies
4
Views
19K
  • Last Post
Replies
1
Views
4K
  • Last Post
Replies
10
Views
5K
  • Last Post
Replies
4
Views
1K
Top