Math Problem Statement

Solve this question in detail. Include all the formulae and calculations involved.

A mass m falls from a height h onto a spring of force constant k. Show that the maximum spring compression is (mg/k) * (1 + sqrt(1 + (2kh/mg))). Show that the maximum speed attained is v = sqrt(2gh(1 + (mg/2kh))). Hint: Use conservation of total mechanical energy.

Solution

Let's solve the given problem step by step. The problem asks us to:

  1. Show that the maximum spring compression is mgk(1+1+2khmg)\frac{mg}{k} \left( 1 + \sqrt{1 + \frac{2kh}{mg}} \right).
  2. Show that the maximum speed attained is v=2gh(1+mg2kh)v = \sqrt{2gh \left( 1 + \frac{mg}{2kh} \right)}, using the principle of conservation of mechanical energy.

Step 1: Maximum Spring Compression

We are given that a mass mm falls from a height hh onto a spring with spring constant kk. To find the maximum compression of the spring, we need to use energy conservation principles.

Energy Consideration:

  • The total mechanical energy at the start (when the mass is at height hh) consists of gravitational potential energy. Einitial=mghE_{\text{initial}} = mgh

  • At the point of maximum compression xmaxx_{\text{max}}, all the potential energy of the mass is converted into elastic potential energy of the spring and some additional gravitational potential energy due to the mass being lower by a distance xmaxx_{\text{max}} (spring compression). Efinal=12kxmax2mgxmaxE_{\text{final}} = \frac{1}{2} k x_{\text{max}}^2 - mgx_{\text{max}}

By conservation of energy: mgh=12kxmax2mgxmaxmgh = \frac{1}{2} k x_{\text{max}}^2 - mgx_{\text{max}}

Rearranging the equation:

12kxmax2mgxmaxmgh=0\frac{1}{2} k x_{\text{max}}^2 - mgx_{\text{max}} - mgh = 0 This is a quadratic equation in xmaxx_{\text{max}}: k2xmax2mgxmaxmgh=0\frac{k}{2} x_{\text{max}}^2 - mgx_{\text{max}} - mgh = 0

Solving the quadratic equation:

The quadratic equation is of the form: Ax2+Bx+C=0Ax^2 + Bx + C = 0 where A=k2A = \frac{k}{2}, B=mgB = -mg, and C=mghC = -mgh.

Using the quadratic formula: xmax=B±B24AC2Ax_{\text{max}} = \frac{-B \pm \sqrt{B^2 - 4AC}}{2A}

Substitute the values of AA, BB, and CC: xmax=(mg)±(mg)24k2(mgh)2k2x_{\text{max}} = \frac{-(-mg) \pm \sqrt{(-mg)^2 - 4 \cdot \frac{k}{2} \cdot (-mgh)}}{2 \cdot \frac{k}{2}} xmax=mg±m2g2+2kmghkx_{\text{max}} = \frac{mg \pm \sqrt{m^2g^2 + 2kmgh}}{k} xmax=mgk(1+1+2khmg)x_{\text{max}} = \frac{mg}{k} \left( 1 + \sqrt{1 + \frac{2kh}{mg}} \right)

Thus, the maximum spring compression is: xmax=mgk(1+1+2khmg)x_{\text{max}} = \frac{mg}{k} \left( 1 + \sqrt{1 + \frac{2kh}{mg}} \right)


Step 2: Maximum Speed

The next part of the question asks us to show that the maximum speed attained by the mass is: v=2gh(1+mg2kh)v = \sqrt{2gh \left( 1 + \frac{mg}{2kh} \right)}

Energy at Maximum Speed:

At the point where the speed is maximum, the mechanical energy consists of both kinetic energy and potential energy. The potential energy stored in the spring is less than at the maximum compression point, which allows for some of the energy to be converted into kinetic energy.

Let the spring compression at this point be xx (not maximum). The conservation of energy gives us: mgh=12kx2+mgx+12mv2mgh = \frac{1}{2} k x^2 + mgx + \frac{1}{2} mv^2

At maximum speed, the kinetic energy 12mv2\frac{1}{2} mv^2 will be maximized, and xx will not be at the maximum compression.

Let’s simplify the equation by considering that at maximum speed, the spring’s potential energy and the gravitational potential energy together allow for the maximum conversion into kinetic energy.

The maximum speed occurs when all the potential energy of the mass from height hh is converted into kinetic energy (ignoring spring compression effects for now): mgh=12mvmax2mgh = \frac{1}{2} mv_{\text{max}}^2 Solving for vmaxv_{\text{max}}: vmax=2ghv_{\text{max}} = \sqrt{2gh}

However, this speed is modified by the influence of the spring. Including the spring’s effect: [ v_{\text{max}} = \sqrt{2gh

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Math Problem Analysis

Mathematical Concepts

Conservation of Energy
Quadratic Equations
Kinetic and Potential Energy

Formulas

Mechanical Energy: E = PE + KE
Gravitational Potential Energy: PE = mgh
Elastic Potential Energy: PE_spring = 1/2 kx^2
Quadratic formula: x = [-b ± sqrt(b^2 - 4ac)] / 2a
Maximum speed: v = sqrt(2gh(1 + (mg/2kh)))

Theorems

Conservation of Mechanical Energy

Suitable Grade Level

Undergraduate Physics