Answer :
Final answer:
The weight of the cheetah at rest would be less than 83 kg, due to the effects of special relativity that only affect the observed mass at high, relativistic speeds.
Explanation:
If a cheetah capable of sprinting at relativistic speeds appears to an observer to weigh 83 kg when she is running at 0.63 c, her weight standing still would actually be less than 83 kg. This is because at relativistic speeds, an object's mass appears to increase due to the effects of special relativity described by Einstein's theory. The mass that the observer measures is the relativistic mass, which includes the increase due to the object's high speed. When the cheetah is at rest, her mass would be her rest mass, which would be less than the relativistic mass observed.
The correct answer to the student's question would therefore be: b) Less than 83 kg.
