• Support PF! Buy your school textbooks, materials and every day products Here!

Physics question on Energy and Spring, any help appreciated

Physics question on Energy and Spring, any help appreciated :D

1. Homework Statement

a. A 1.0 kg puck sliding at 15 m/s along some horizontal frictionless ice strikes and compresses a horizontal spring attached to one end of the ice rink. If the spring has a constant of 35 N/m, what is the maximum compression of the spring?

b. If in the above problem, the puck experiences a constant frictional force of 4.0 N opposing its motion beginning when it first strikes the spring, what would the maximum compression of the spring now be? (10 marks)


I am unsure about part b, as i am not sure what to use for the value of Δd as you will see underneath at my attempt

2. Homework Equations

-0.5mv^2 (1) + 0.5kv^2 (1)= 0.5mv^2 (1) + 0.5kv^2 (1)

- E(thermal) = Frictional force x Δd

3. The Attempt at a Solution

E(total 1) = E (total 2)
0.5mv^2 (1) + 0.5kv^2 (1)= 0.5mv^2 (1) + 0.5kv^2 (1) [ 0.5kv^2 (1) and 0.5mv^2 (1) equal 0]
0.5mv^2 (1) = 0.5kv^2 (1)
x = √((15^2)/35)
x = 2.535 m


[ (1) <-- denotes to initial (2)<-- denotes to final]

Part b
E(total 1) = E (total 2)
0.5mv^2 (1) + 0.5kv^2 (1)= 0.5mv^2 (1) + 0.5kv^2 (1) + E(thermal) [ 0.5kv^2 (1) and 0.5mv^2 (1) equal 0]
0.5mv^2 (1) = + 0.5kv^2 (1) + Ff Δ d

I am unsure of what to do from here

[ (1) <-- denotes to initial (2)<-- denotes to final]
 

cepheid

Staff Emeritus
Science Advisor
Gold Member
5,183
35
Re: Physics question on Energy and Spring, any help appreciated :D

The amount by which the spring compresses, x, is the same as the distance over which work is done by friction, which you have called Δd.

Oh, and by the way, the elastic potential energy is given by (1/2)kx2. (It should be an x, not a v).
 
Re: Physics question on Energy and Spring, any help appreciated :D

Oh yes, i meant kx :P
thank you for that

But why would Δd be the x value from part a?
 

cepheid

Staff Emeritus
Science Advisor
Gold Member
5,183
35
Re: Physics question on Energy and Spring, any help appreciated :D

Oh yes, i meant kx :P
thank you for that

But why would Δd be the x value from part a?
Δd is not the x value from part a. Δd is the x value from part b! :tongue2:

The reason is because the frictional force starts up at the instant that the object touches the spring. So the distance over which the spring is compressed (before the thing comes to a stop) is the same as the distance over which the friction acts.
 
Re: Physics question on Energy and Spring, any help appreciated :D

Ohhhhhh Thank youu so much!!
I was really confused with that question lol
 

Related Threads for: Physics question on Energy and Spring, any help appreciated

Replies
3
Views
3K
Replies
5
Views
1K
Replies
16
Views
2K
  • Last Post
Replies
7
Views
2K
Replies
8
Views
1K
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
1
Views
715
  • Last Post
Replies
1
Views
4K
Top