An astronaut at rest on Earth has a heart rate of 70
Chapter 26, Problem 26.24(choose chapter or problem)
An astronaut at rest on Earth has a heart rate of 70 beats/min. When the astronaut is traveling in a spaceship at 0.90c, what will this rate be as measured by (a) an observer also in the ship and (b) an observer at rest on Earth?
Unfortunately, we don't have that question answered yet. But you can get it answered in just 5 hours by Logging in or Becoming a subscriber.
Becoming a subscriber
Or look for another answer