The speed of light and relativity

Answer Key - Grade 11 Science Worksheet

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

1. 1.

   A muon at rest lives 2.197 μs on average (PDG). Measured from the ground, how long does one moving at 0.99c last, to 0.01 μs, Ari?

   15.57 μs
2. 2.

   A muon at rest lives 2.197 μs on average (PDG). Measured from the ground, how long does one moving at 0.98c last, to 0.01 μs, Esme?

   11.04 μs

3. Read this first

   GPS satellite clocks compared with ground clocks (from Ashby's fractional rates × 86,400 s)

   Effect	Change in the satellite clock (μs per day)
   Weaker gravity at its height	+45.7
   Its orbital speed	-7.1
   Net	+38.6

4. 3.

   Using the table, does a GPS satellite clock run fast or slow overall, compared with ground clocks, Jun?

   • The two effects cancel exactly
   • Fast, by about 38.6 μs a day
   • Slow, by about 38.6 μs a day
5. 4.

   Using the table, why does the satellite's speed make its clock lose time, Kira?

   • Space is colder than the ground
   • Moving clocks tick slower
   • Its batteries run down
6. 5.

   Using the table, why does the satellite's height make its clock gain time, Luz?

   • Its speed makes it run fast
   • It is closer to the Sun
   • Gravity is weaker up there
7. 6.

   A rod moves past at 0.8c. Measured from the ground, how long is it along its motion, Milo?

   • Shorter than at rest
   • Exactly as long as at rest
   • Longer than at rest
8. 7.

   Muons made high in the air reach the ground in large numbers. Why, Noah?

   • Air makes them live longer
   • They travel faster than light
   • Their lifetimes are stretched
9. 8.

   Two matched clocks: one rides a fast rocket and returns, one stays put. Ignoring gravity, which shows less time, Pia?

   • They show the same time
   • The one that rode the rocket
   • The one that stayed put
10. 9.

    As an object gets close to c, what happens to the energy needed to speed it up more, Ren?

    • It stays the same
    • It grows without limit
    • It drops to zero
11. 10.

    Sunlight takes about 499 seconds to reach Earth. What does this show, Zee?

    • Light arrives instantly
    • Sunlight slows down in space
    • Light's speed is finite