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 0.995c last, to 0.01 μs, Bo?

   22 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?

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

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

   • Exactly as long as at rest
   • Shorter than at rest
   • Longer than at rest
7. 6.

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

   • Their lifetimes are stretched
   • Air makes them live longer
   • They travel faster than light
8. 7.

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

   • The one that stayed put
   • The one that rode the rocket
   • They show the same time
9. 8.

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

   • It drops to zero
   • It stays the same
   • It grows without limit
10. 9.

    Can a particle accelerator push a proton to the speed of light, Tala?

    • Yes, if its ring is big enough
    • Yes, at full power
    • No: close to c, but not to it
11. 10.

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

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