Chapter 10 review Special relativity: Length, momentum & energy

The resolution to the twins’ paradox lies in

the observation that:

• no two people can be exactly the same age.

• the twin who stays on Earth ages

  differently because of Earth’s

  gravitational field.

• the predictions of special relativity only

  apply to subatomic particles.

• one of the twins must accelerate in order

  to leave Earth and come back.

Select the statement about which all observers in different inertial systems will agree.

• the simultaneity of events at separate locations

• the rate at which their clocks run

• the lengths they measure along the direction of their relative travel

• they will agree on none of the above

A meteor is heading directly towards the surface of a planet at a constant speed of 0.8c. Observers on the surface of the planet observe it at a time when it is a distance h above the surface in their reference frame. The observers calculate the time that the meteor will take to reach the surface of the planet as 784 μs.

The value that is closest to the distance h is:

• 105 km

• 200 km

• 235 km

• 380 km

The relativistic momentum of an atomic particle of mass 1.62 × 10–27 kg moving at 0.92c is:

• 3.80 × 10–27 kg m s–1

• 9.70 × 10–27 kg m s–1

• 1.14 × 10–18 kg m s–1

• 2.91 × 10–18 kg m s–1

The rest energy, in joules, of an electron of mass 9.11 × 10–31 kg is:

• 3.0 × 10–39 J

• 2.7 × 10–22 J

• 8.2 × 10–14 J

• 1.1 × 10–11 J

Calculate the speed of a pion if its rest life is 2.6 × 10–8 s but to a laboratory observer it appears to live for
5.2 × 10–8 s. (answer in c, 2sf)