The speed of light and relativity

Answer Key - Grade 11 Science Worksheet - Building Confidence

Circle the best answer, or write your answer on the line.

1. 1.

   A particle moves at 0.6c. Using γ = 1 ÷ √(1 − v²/c²), what is γ, to 0.01, Ari?

   1.25
2. 2.

   A particle moves at 0.8c. Using γ = 1 ÷ √(1 − v²/c²), what is γ, to 0.01, Bo?

   1.67
3. 3.

   A particle moves at 0.96c. Using γ = 1 ÷ √(1 − v²/c²), what is γ, to 0.01, Esme?

   3.57

4. Read this first

   Photon diagram with two observers

   Observer A rides a train moving at 0.6c, holding a light clock where light bounces between two mirrors. Observer B stands beside the track. Both measure the light's speed as c. B sees the light take a longer, slanted path, so B sees A's clock tick slower.

5. 4.

   In the photon diagram, what speed does B measure for the light in A's clock, Jun?

   • c − 0.6c
   • c + 0.6c, adding the train's speed
   • c, the same as A measures
6. 5.

   In the photon diagram, whose clock does B see ticking slower, Kira?

   • A's clock on the train
   • B's own clock
   • Both tick at the same rate
7. 6.

   In the photon diagram, why does B see each tick take longer, Luz?

   • The light slows down
   • B's eyes see light more slowly
   • The light's path is longer
8. 7.

   A train's headlight shines forward as it moves. How fast does the light leave, measured from the ground, Noah?

   • c, the same as from a still lamp
   • c minus the train's speed
   • c plus the moving train's own speed
9. 8.

   What does special relativity say about time, Ren?

   • Time stops on trains
   • Time runs alike in each frame
   • Moving clocks run slow
10. 9.

    Why don't we notice time slowing on a moving bus, Tala?

    • Buses are too heavy for it
    • The bus's air slows the effect down
    • Its speed is tiny compared with c
11. 10.

    Can a rocket ever reach the speed of light, Zee?

    • Yes, with a big enough engine
    • Yes, if it speeds up for years
    • No: nothing with mass can