Answer:

Explanation:
As we know that when runner is moving on straight track then the net force on his feet is given as

while when runner is moving on circular track then we have




now percentage change is given as



The answer to your question is b
The term period (symbol: T) describes the time it takes for an object to complete one full cycle of motion on a spring.
The formula for time is: T = 1 / f , where f is the frequency , f= c / λ = wave speed c (m/s) / wavelength λ (m)..
The formula describes that as the frequency of a wave increases, the time period of the wave decreases.
Helium only has 2 electrons. So the answer is C. 2