# Length contraction & relativistic momentum, mass and energy

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##### Intros

##### Examples

###### Lessons

- A star is 62 light-years away in the Earth frame of reference. How fast would you have to travel so that to you the distance is only 15 light-years?
- Suppose you decided to travel to a star 60 light-years away at a speed that tells you the distance is only 15 light-years. How many years would it take to make the trip?
- At what speed will the length of a 1.00m stick look 20.0% shorter?
- The length of a ruler placed in spaceship in 32cm. The spaceship moves with a speed of 0.080c. what would be the percent decrease in the length of the ruler?
- What is the relativistic momentum of an antiproton moving at a speed of 0.68c and mass of 1.674 x 10
^{-27}kg? - What is the percentage change in the momentum of an electron that accelerates from 0.25c to 0.80c? (mass of electron = 9.12 x 10
^{-31}kg) - Calculate the rest energy of an electron in joules and in Mev

(1Mev= 1.60 x 10^{-13}J) - What would be the momentum and kinetic energy of a proton travelling with a speed of 1.80 x 10
^{8}m/s. (Proton rest mass = 1.67 x 10^{-27}kg) - Calculate the kinetic energy and momentum of a proton travelling 6.24 x 10
^{7}m/s. What would be the percentage error if the value was calculated using classical formula? - A person on a spaceship traveling at 0.60c (with respect to the Erath) observers a comet come from behind and pass her at a speed of 0.60c. how fast is the comet moving with respect to the Earth?
- A spaceship leaves the Earth traveling at 0.61c. A second spaceship leaves the first at a speed of 0.77c with respect to the first one. Calculate the speed of the second spaceship with respect to the earth if it is fired
- In the same direction the first spaceship is already moving
- Directly backwards towards the Earth