Obtain the relation between the total kinetic energy in the CM and Lab frames. Discuss the limiting cases of very large and very small mass for the target.

Short Answer

Expert verified
Answer: The total kinetic energy in the center of mass frame and the lab frame are related by the expression KE_lab - KE_cm = 0.5*(m1*m2)/(m1+m2) * (V1 - V2)^2. For very large target mass, a large amount of kinetic energy is associated with the internal motion of the system. In contrast, for very small target mass, very little kinetic energy is associated with the internal motion of the system.

Step by step solution

01

Define the Center of Mass Frame and Lab Frame

First, let's define the two frames of reference involved in this problem. - Center of Mass Frame (CM): In this frame, the total momentum is always zero. The coordinate system is defined with its origin at the center of mass of the system. - Lab Frame: This frame is an observer's frame of reference, typically stationary relative to the observer (e.g., the Earth). Now let's identify the system we will be using in this problem, which will be a collision between two particles, one with mass m1 and the other with mass m2.
02

Find velocities and momenta in both frames

Let's assume that the velocities of the two particles in the lab frame are V1 and V2. Then the momenta are P1 = m1*V1 and P2 = m2*V2. The total momentum in the lab frame is P = P1 + P2. Now, we change to the center of mass frame. We subtract the velocity of the CM frame v_cm from V1 and V2 to obtain velocities of particles in the CM frame: U1 = V1 - v_cm, U2 = V2 - v_cm. The momenta in the CM frame will be M1 = m1*U1 and M2 = m2*U2. By definition, the total momentum in CM frame must be 0, so we find: M1 + M2 = m1*U1 + m2*U2 = 0
03

Compute the total kinetic energy in the lab and CM frames

Now we calculate the total kinetic energy (KE) in the lab frame and CM frame. For the lab frame: KE_lab = 0.5*m1*(V1^2) + 0.5*m2*(V2^2) For the CM frame: KE_cm = 0.5*m1*(U1^2) + 0.5*m2*(U2^2)
04

Relate the total kinetic energy in the lab and CM frames

First, express U1 and U2 in terms of V1, V2, and v_cm: U1 = V1 - v_cm U2 = V2 - v_cm Now substitute these expressions into the KE_cm formula: KE_cm = 0.5*m1*((V1 - v_cm)^2) + 0.5*m2*((V2 - v_cm)^2) Subtract KE_cm from KE_lab to eliminate v_cm: KE_lab - KE_cm = 0.5*m1*(V1^2) + 0.5*m2*(V2^2) - [0.5*m1*((V1 - v_cm)^2) + 0.5*m2*((V2 - v_cm)^2)] Simplify the expression to find the relationship between KE_lab and KE_cm: KE_lab - KE_cm = 0.5*(m1*m2)/(m1+m2) * (V1 - V2)^2
05

Discuss the limiting cases of large and small target mass

For the limiting cases of very large and very small mass for the target (m2), we discuss how the total kinetic energy is affected in each case. 1. Very large target mass (m2 >> m1): The fraction (m1*m2)/(m1+m2) will approach m1, thus making the quantity (KE_lab - KE_cm) larger. In this case, a large amount of kinetic energy is associated with the internal motion of the system. 2. Very small target mass (m1 >> m2): The fraction (m1*m2)/(m1+m2) will approach m2, thus making the quantity (KE_lab - KE_cm) smaller. In this case, very little kinetic energy is associated with the internal motion of the system. In summary, the relationship between the total kinetic energy in the center of mass frame and the lab frame is given by the expression: KE_lab - KE_cm = 0.5*(m1*m2)/(m1+m2) * (V1 - V2)^2 For very large and very small target mass, we discussed the implications of the kinetic energy being more or less associated with the internal motion of the system.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with Vaia!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

Two particles of masses \(m_{1}\) and \(m_{2}\) are attached to the ends of a light spring. The natural length of the spring is \(l\), and its tension is \(k\) times its extension. Initially, the particles are at rest, with \(m_{1}\) at a height \(l\) above \(m_{2} .\) At \(t=0, m_{1}\) is projected vertically upward with velocity \(v\). Find the positions of the particles at any subsequent time (assuming that \(v\) is not so large that the spring is expanded or compressed beyond its elastic limit).

An experiment is to be designed to measure the differential cross-section for elastic pion-proton scattering at a CM scattering angle of \(70^{\circ}\) and a pion CM kinetic energy of \(490 \mathrm{keV}\). (The electron-volt \((\mathrm{eV})\) is the atomic unit of energy.) Find the angles in the Lab at which the scattered pions, and the recoiling protons, should be detected, and the required Lab kinetic energy of the pion beam. (The ratio of pion to proton mass is \(1 / 7\).)

An unstable particle of mass \(M=m_{1}+m_{2}\) decays into two particles of masses \(m_{1}\) and \(m_{2}\), releasing an amount of energy \(Q .\) Determine the kinetic energies of the two particles in the CM frame. Given that \(m_{1} / m_{2}=4, Q=1 \mathrm{MeV}\), and that the unstable particle is moving in the Lab with kinetic energy \(2.25 \mathrm{MeV}\), find the maximum and minimum Lab kinetic energies of the particle of mass \(m_{1}\).

Write down the equations of motion for a pair of charged particles of equal masses \(m\), and of charges \(q\) and \(-q\), in a uniform electric field \(\boldsymbol{E}\). Show that the field does not affect the motion of the centre of mass. Suppose that the particles are moving in circular orbits with angular velocity \(\omega\) in planes parallel to the \(x y\)-plane, with \(\boldsymbol{E}\) in the \(z\)-direction. Write the equations in a frame rotating with angular velocity \(\omega\), and hence find the separation of the planes.

The parallax of a star (the angle subtended at the star by the radius of the Earth's orbit) is \(\varpi\). The star's position is observed to oscillate with angular amplitude \(\alpha\) and period \(\tau\). If the oscillation is interpreted as being due to the existence of a planet moving in a circular orbit around the star, show that its mass \(m_{1}\) is given by \(\frac{m_{1}}{M_{\mathrm{S}}}=\frac{\alpha}{\varpi}\left(\frac{M \tau_{\mathrm{E}}}{M_{\mathrm{S}} \tau}\right)^{2 / 3}\) where \(M\) is the total mass of star plus planet, \(M_{\mathrm{S}}\) is the Sun's mass, and \(\tau_{\mathrm{E}}=1\) year. Evaluate the mass \(m_{1}\) if \(M=0.25 M_{\mathrm{S}}, \tau=16\) years, \(\varpi=0.5^{\prime \prime}\) and \(\alpha=0.01^{\prime \prime} .\) What conclusion can be drawn without making the assumption that the orbit is circular?

See all solutions

Recommended explanations on Physics Textbooks

View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free