Question

Two blocks are on a frictionless, horizontal surface. Block II is stationary and has a spring attached facing block I, which approaches with a speed v. The spring compression is a maximum when the blocks have the same velocity. Briefly explain why this is so.

Answer 1

use momentum conservation equations or solve the problem using the concept of reduced mass from the cm frame...

Answer 2

no I figured out the different velocities and the compression I need to know why the max compression is when they are at the same velocity, I need a conceptual explanation rather than the computational one.

Answer 3

actually this result comes only when you solve it that way, there is no perfect conceptual reason for it, it is just the way nature works and you get to know that by solving some trivial equations

Answer 4

would it have anything to do with it being an elastic collision and that this may be the point in which the most kinetic energy has been converted in potential energy in the spring?

Answer 5

the 2 blocks will never collide with each other.

Answer 6

yes but I mean as a system it would be an elastic collision, such as if block II is thought of as a whole object not as a block and spring, it would be an elastic collision between the two systems

Answer 7

yes it will be elastic just to say that energy is not lost when the block collides with the spring...

Answer 8

and the energy would briefly be transferred into potential energy of the spring due to compression so when the velocities are the same that would mean the spring has its max potential energy is there a reason for that?

Answer 9

yes correct..

Answer 10

but is there a reason it happens at that moment?

Answer 11

no it just comes that way naturally and that is what the equations tell, due to the spring the first block slows and the second block fastens and it so becomes tht the compression is max, when both have the same velocity.

Answer 12

I see I understand what you mean I'm just trying to put that in terms of an explanation of the equations since I can see the graph of it but I'm having trouble putting it into a conceptual explanation past thats just the way it works.

Answer 13

strange but true,

Answer 14

ok thank you I'll try and go from there and I'll come back if anything else comes up thanks for your help.

Answer 15

welcome. where are you from ?

Answer 16

i mean which school ?

Answer 17

im still in high school this is for a physics ap course

Answer 18

in the united states ?

Answer 19

yes

Answer 20

which school are you from?

Answer 21

It is because when both blocks are of the same velocity, their relative speed to each other is zero. I.e. The block does not see the other block moving. It is impossible to have the blocks phase through each other so their relative velocity at that time must be same, i.e. zero. When such an event happens, it also happens that the spring cannot be compressed further.
Do you follow?

Answer 22

his question is why cant the spring compress further when such an event takes place?

Answer 23

As said, during that even, due to the blocks unable to phase into each other, the spring will not compress further. The blocks cannot go into one another.

Answer 24

Naturally, from logic, since the blocks cannot go into each other, they have to bounce away. So, during that time, the spring is max. compressed.

Answer 25

during such a collision the maximum compression doesnt mean that the spring is totallly compressed, it is the highest limit that the spring is compressed with the particular given speed of the blocks...

Answer 26

Yes, that's why the choice of words is max. compression. :)

Answer 27

yes that word is quite misleading...