- #1

student07

- 36

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## Homework Statement

The proper length of a spaceship A is 60 m and the proper length of spaceship B is 120 m. The proper mass of spaceship A is 15000 kg. An observer on Earth watches the two spaceships fly past at a constant speed and determines that they have the same length. If the speed on the slower spaceship is 0.70 c, find:

a) the length of spaceship A, relative to an observer on earth.

b) the speed of spaceship B, relative to an observer on earth.

c) the mass of spaceship A, relative to an observer on earth.

**2. The attempt at a solution**

a) Lm = Ls√(1- V^2 / C^2)

= 60√(1- (0.70 c) ^2 / C^2

= 60√(1-0.49) = 42.85 = 43 m

b) I'm not sure how to solve this one, I have seeing some suggestions like:

120 / 43 = 2.8 but I don't see the connection

also √{1 - (v/c)²}x120, giving v=0.9341c. but the result makes no sense

any help or equation that I can use would be appreciated

c) Mm = Ms / √(1- V^2 / C^2)

= 15000 kg / √(1-0.70 c)^2 / C^2 = 21004 = 2.1 x 10^4 kg