At stp (standard temperature and pressure), the temperature is T=0 C=273 K and the pressure is p=1.00 atm. So we can use the ideal gas law to find the number of moles of helium:

where p is the pressure (1.00 atm), V the volume (20.0 L), n the number of moles, T the temperature (273 K) and

the gas constant. Using the numbers and re-arranging the formula, we can calculate n:
Answer:
V = V_0 - (lamda)/(2pi(epsilon_0))*ln(R/r)
Explanation:
Attached is the full solution
Answer:
v= 335 m/s
2∆t= 0.75 s
∆x= v.∆t → ∆x= 335×½×0.75 = 125.625 m
One should check the battery every week.
A battery if not maintained properly can cause it to die earlier or get damaged. The reasons why should the battery be checked regularly is that due to improper management of the battery and also the weather conditions, the battery usually gets corroded easily and the battery won't be able to work properly.
The connections must be checked properly so that the battery gets charged properly and should not die while driving.