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I think it belong to Introductory Physics homehork, it's my first course college's physics course, I think it's pretty basic.

We have particle 1 with a mass of 1.6 KG (left one), and particle 2 with an attached spring to it's left with a mass of 2.1 KG (right one).

[Broken]

They're both in a frictionless floor.

The particle 1 has a speed of 4 m/s, and the particle 2 has a speed of -2.5 m/s (they are in the same line).

The spring has a constant of 600 N/m

If someone knows a good way to make sketchs involving springs in the computer I'll try to draw it, if the problem isn't clear I'll scan the sketch.

(a) After the spring starts to shrink, at certain time the particle 1 has a speed 3 m/s. What speed has the particle 2 at the same time?

(b) How much has the spring shrink at that time?.

I know how to solve problems involving an immovable spring, but in this problem I always end up making an assumption I don't know how to justify in order to solve it.

I know:

[itex]\Delta U_e+\Delta U_c+\Delta U_g=0[/itex]

[itex]U_e=k x^2[/itex]

[itex]U_c=\sum_{i=1}^{n} \frac{1}{2}v_i ^2m_i[/itex]

[itex]U_g=0[/itex] this isn't used in this problem.

I can calculate how much will the spring shrink at the most because I can think the mass 2 as point of reference and mass 1 with a speed of 6.5 m/s, but I don't know how to solve this without making, for example, the assumption that the spring absorvs energy at the same rate from both sides.

We have particle 1 with a mass of 1.6 KG (left one), and particle 2 with an attached spring to it's left with a mass of 2.1 KG (right one).

[Broken]

They're both in a frictionless floor.

The particle 1 has a speed of 4 m/s, and the particle 2 has a speed of -2.5 m/s (they are in the same line).

The spring has a constant of 600 N/m

If someone knows a good way to make sketchs involving springs in the computer I'll try to draw it, if the problem isn't clear I'll scan the sketch.

(a) After the spring starts to shrink, at certain time the particle 1 has a speed 3 m/s. What speed has the particle 2 at the same time?

(b) How much has the spring shrink at that time?.

I know how to solve problems involving an immovable spring, but in this problem I always end up making an assumption I don't know how to justify in order to solve it.

I know:

[itex]\Delta U_e+\Delta U_c+\Delta U_g=0[/itex]

[itex]U_e=k x^2[/itex]

[itex]U_c=\sum_{i=1}^{n} \frac{1}{2}v_i ^2m_i[/itex]

[itex]U_g=0[/itex] this isn't used in this problem.

I can calculate how much will the spring shrink at the most because I can think the mass 2 as point of reference and mass 1 with a speed of 6.5 m/s, but I don't know how to solve this without making, for example, the assumption that the spring absorvs energy at the same rate from both sides.

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