5.2 Relativity of Time, Length, and Momentum

There are two clocks one is stationary on the earth the other is traveling close to the speed of light around the earth. If we put the clocks back together after the second clock makes it back from its trip, the times are compared. What do you expect to occur?

• More time elapsed on the stationary clock

• More time elapsed on the traveling clock

• No time has changed between them

Based on the concepts of Special Relativity time travel is...

• not possible

• possible only in the ability to travel into the past.

• possible only in the ability to travel to the future.

• possible to travel either forward or backward in time.

Which of the following statements is not true according to the theory of relativity? 

• As an object increases speed its mass increases. 
• As an object increases speed its length increases. 
• As an object increases speed its kinetic energy increases. 
• As an object increases speed its momentum increases. 

We do not usually observe relativistic effects in our daily lives because 

• we are moving at speeds much less than c. 
• we are much larger than atoms. 
• we are much heavier than elementary particles. 
• we are much lighter than stars. 

Lachlan's spaceship takes a nonstop journey to a planet and returns in 10 hours according to a clock on the spaceship. If the speed of the spaceship is 0.80c, how much time has elapsed on the Earth?

• 3.2h

• 7.0h

• 15h

• 17h

A meter stick is moving toward you with a speed of 0.80c. What is its length?

• zero

• 0.40m

• 0.60m

• 1.0m

An observer notices that a clock moving with a speed of 0.650c advances 2.00 seconds. How much time elapses on the identical clock at rest?

• 1.52 seconds

• 2.97 seconds

• 2.63 seconds

• 2.00 seconds

How long is a plank of wood at rest if its length when moving at 0.995c is 2.00 m?

• .19974 m

• 20.0447 m

• 20.19974 m

• 0.0447 m

A set of twins, Abbey and Angelina, are initially 10 years old. While Angelina remains on Earth, Abbey rides on a space ship which travels away from Earth at a speed of 0.6c for five years (as measured by Angelina), then turns around and comes back at 0.6c. When Abbey returns, Angelina is 20 years old. How old is Abbey upon her return?

• 10

• 12

• 18

• 20

At one point in time, two twins are 30 years old. At this time, one of them gets on a rocket and travels at 0.8 c, for what he experiences to be 12 years. How old is the twin that remained on Earth when the traveling twin returns home?

• 20 years

• 50 years

• 40 years

• 80 years