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# Relativistic momentum and relativistic energy

الكلية كلية التربية للعلوم الصرفة     القسم قسم الفيزياء     المرحلة 3
أستاذ المادة فؤاد عطية مجيد       14/12/2016 10:46:59
An observer on Earth sees a spaceship at an altitude of 4350 km moving
downward toward Earth with a speed of 0.970c. What is the distance
from the spaceship to Earth as measured by the spaceship’s captain?
(b) After firing his engines, the captain measures her ship’s altitude as 267
km, while the observer on Earth measures it to be 625 km. What is the
speed of the spaceship at this instant?

Solution
(a) Find the distance from the ship to Earth as measured by the captain.
Substitute into Equation 7.11, getting the altitude as measured by the captain
in the ship.

(b) What is the subsequent speed of the spaceship if the Earth observer
measures the distance from the ship to Earth as 625 km and the captain
measures it as 267 km?

Relativistic momentum and relativistic energy
Properly describing the motion of particles within the framework of
special relativity requires generalizing Newton’s laws of motion and the
definitions of momentum and energy. These generalized definitions reduce to
the classical (nonrelativistic) definitions when u is much less than c.
p=mu (for classical physics)
We have seen that the definition of momentum required generalization to
make it compatible with the principle of relativity. Likewise, the definition of
kinetic energy requires modification in relativistic mechanics. Einstein found
that the correct expression for the kinetic energy of an object is
The constant term m c2 o in Equation 7.13, which is independent of the speed
of the object, is called the rest energy of the object, ER:
Example: 2
An electron moves with a speed u = 0.850c. Find its total energy and kinetic
energy in mega electron volts (MeV), and compare the latter to the classical
kinetic energy (106 eV= 1 MeV).
Solution:

المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .