Math Problem Statement

Ein Block mit einer Masse m1 gleitet mit der Geschwindigkeit v1 über eine reibungsfreie Tischplatte auf einen zweiten Block mit der Masse m2 zu. Eine Feder, die sich nach dem Hooke'schen Gesetz verhält und eine Federkonstante k hat, ist so an dem zweiten Block angebracht, dass sie zusammengedrückt wird, wenn der erste Block auf sie trifft. Begründen Sie, ob der Stoß elastisch ist oder nicht. Um welchen Betrag wird die Feder bei dem Stoß maximal zusammengedrückt? Wie groß sind die Endgeschwindigkeiten der Blöcke nach dem Stoß?

Solution

The task involves analyzing a collision with a spring ("Stoß mit Feder"). I'll solve this step by step:

Problem Overview:

We have two blocks:

  • Block 1: Mass m1m_1, moving with initial velocity v1v_1.
  • Block 2: Mass m2m_2, initially at rest.
  • A spring (with spring constant kk) is attached to Block 2. The spring compresses as Block 1 collides with Block 2. The system is frictionless.

We need to:

  1. Determine if the collision is elastic or not.
  2. Calculate the maximum compression of the spring during the collision.
  3. Compute the final velocities of both blocks after the collision.

Solution Steps:

a) Is the collision elastic or not?

The collision is elastic if:

  • Kinetic energy is conserved.
  • Momentum is conserved.

Since no energy is lost (e.g., to heat or deformation), and the system has a frictionless surface, the collision is elastic.


b) Maximum compression of the spring (xmaxx_{\text{max}}):

During maximum compression:

  • Both blocks move with the same velocity vcommonv_{\text{common}} (relative velocity is zero at this point).
  • Use conservation of momentum to find vcommonv_{\text{common}}: m1v1=(m1+m2)vcommonm_1 v_1 = (m_1 + m_2) v_{\text{common}} vcommon=m1v1m1+m2v_{\text{common}} = \frac{m_1 v_1}{m_1 + m_2}

Now, consider the kinetic energy lost during compression. This energy is converted into potential energy of the spring: ΔE=12m1v1212(m1+m2)vcommon2\Delta E = \frac{1}{2} m_1 v_1^2 - \frac{1}{2} (m_1 + m_2) v_{\text{common}}^2 ΔE=12kxmax2\Delta E = \frac{1}{2} k x_{\text{max}}^2

Substitute vcommonv_{\text{common}} into ΔE\Delta E: 12m1v1212(m1+m2)(m1v1m1+m2)2=12kxmax2\frac{1}{2} m_1 v_1^2 - \frac{1}{2} (m_1 + m_2) \left(\frac{m_1 v_1}{m_1 + m_2}\right)^2 = \frac{1}{2} k x_{\text{max}}^2

Solve for xmaxx_{\text{max}}: xmax=m1m2v12k(m1+m2)x_{\text{max}} = \sqrt{\frac{m_1 m_2 v_1^2}{k (m_1 + m_2)}}


c) Final velocities of the blocks (v1v_1', v2v_2'):

Using the equations for an elastic collision:

  1. v1v_1' (final velocity of m1m_1): v1=m1m2m1+m2v1v_1' = \frac{m_1 - m_2}{m_1 + m_2} v_1
  2. v2v_2' (final velocity of m2m_2): v2=2m1m1+m2v1v_2' = \frac{2 m_1}{m_1 + m_2} v_1

Final Results:

  1. The collision is elastic.
  2. Maximum spring compression: xmax=m1m2v12k(m1+m2)x_{\text{max}} = \sqrt{\frac{m_1 m_2 v_1^2}{k (m_1 + m_2)}}
  3. Final velocities of the blocks: v1=m1m2m1+m2v1v_1' = \frac{m_1 - m_2}{m_1 + m_2} v_1 v2=2m1m1+m2v1v_2' = \frac{2 m_1}{m_1 + m_2} v_1

Would you like further details on any of these steps?

Related Questions:

  1. How is energy conserved during a perfectly elastic collision?
  2. How would adding friction affect the system's outcome?
  3. What happens if the collision is perfectly inelastic instead of elastic?
  4. Can the spring constant kk influence the final velocities of the blocks?
  5. What role does the mass ratio m1/m2m_1/m_2 play in the collision dynamics?

Tip:

In elastic collisions, the relative velocity of the two objects before and after the collision is equal in magnitude but opposite in direction!

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Math Problem Analysis

Mathematical Concepts

Elastic Collisions
Conservation of Energy
Conservation of Momentum
Hooke's Law

Formulas

v_common = (m1 * v1) / (m1 + m2)
x_max = sqrt((m1 * m2 * v1^2) / (k * (m1 + m2)))
v1' = ((m1 - m2) / (m1 + m2)) * v1
v2' = (2 * m1 / (m1 + m2)) * v1

Theorems

Conservation of Momentum
Conservation of Kinetic Energy in Elastic Collisions

Suitable Grade Level

Grades 11-12